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README.bigb

= OurBigBook
{c}
{title2=previously Cirodown}

https://ourbigbook.com source code + a compatible local CLI static wiki generator and markup language to write complex structured wikis/books/blogs with reference implementation in JavaScript.

This repository (The OurBigBook Project) contains two main things:
* \x[ourbigbook-cli]: a static Wiki generator that can be invoked from the command line with the \x[ourbigbook-executable]. The OurBigBook CLI calls the \x[ourbigbook-library] to convert each input file.

The markup language used is called \x[ourbigbook-markup] (file extension: `.bigb`), and it is compatible with https://ourbigbook.com[], TODO support import/export to/from https://ourbigbook.com[] to local filesystem.
* \x[ourbigbook-web]: the source code of https://ourbigbook.com[], which is a regular database-backed dynamic website. This is basically separate package that depends on the OurBigBook Library:
* information about OurBigBook Web is present at: \x[ourbigbook-web]{full}
* the source code of the OurBigBook Web is present under `web/`
Everything else in this repository outside of that section/directory is about the OurBigBook Library and the OurBigBook CLI, not the dynamic website.

Key links:
* https://cirosantilli.com[]: showcase demo document with interesting content. Primary inspiration for OurBigBook development.
* https://cirosantilli.com/oxford-nanopore-river-bacteria[]: a self-contained tutorial style part of the above. Note how internal links integrate seamlessly into the more global topic of biology, e.g. when talking about DNA we link to the global topic https://cirosantilli.com/dna[].
* https://github.com/cirosantilli/cirosantilli.github.io[] and https://github.com/cirosantilli/cirosantilli.github.io/blob/dev/oxford-nanopore-river-bacteria.bigb[]: source of the above showcase documents
* \x[design-goals]{full}: feature overview
* https://github.com/cirosantilli/ourbigbook[]: OurBigBook source code
* https://github.com/cirosantilli/ourbigbook/blob/master/README.bigb[]: source for this document
* https://cirosantilli.com/ourbigbook[]: rendered version of this document
* https://cirosantilli.com/ourbigbook/editor[]: live in-browser demo
* https://cirosantilli.com/ourbigbook-template[]: good template to get started, see \x[quick-start]{full}

= Features
{parent=ourbigbook}

* \x[internal-cross-reference][references] to any \x[header]{p} (including e.g. h2, h3, etc. in other files), \x[image]{p}, etc. with amazing \x[error-reporting][error checking and reporting]: never break internal links without knoing again, and quickly find out what broke when you do. E.g.:

README.bigb
``
= My website

See: \x[not-readme], or \x[not-readme-h2].
``
not-readme.bigb
``
= Not readme

== Not readme h2
``
`README.bigb` would render something like:
``
See: not readme, or not readme.
``
The following would fail and point you out the file and line of the failure:
* nonexistent id:
``
\x[id-that-does-not-exist]
``
* duplicate IDs:
``
= My h1

== My h2

== My h2
``
* https://katex.org/[KaTeX] server side \x[mathematics], works on browsers with JavaScript disabled:
``
I like $\sqrt{2}$, but I adore this \x[equation-quadratic-equation]:

$$
x^2 + 2x + 1
$$
{title=Quadratic equation}
``
* multi-file features out of the box so you don't need a separate wrapper like Jekyll to make a multi-page website:
* \x[internal-cross-file-reference]{p}
* single-source multi-format output based on \x[include]{p} and build options:
* by default, one HTML per source with includes rendered as links between pages, e.g.:

README.bigb
``
= My website

== h2

\Include[not-readme]
``
not-readme.bigb
``
= Not readme

== Not readme h2
``
produces `index.html` and `not-readme.html`
* with the \x[split-headers] option, you can output each header of an input file into a separate output file. The previous filesystem would produce:
* `index.html`: which contains the full `README.bigb` output
* `split.html`: split version of the above containing only the `= My website` header and not `h2`
* `h2.html`: only contains the `h2` header
* `not-readme.html` contains the full output of `not-readme.bigb`
* `not-readme-split.html`: only contains the `= Not readme` header
* `not-readme-h2.html`: only contains the `= Not readme h2` header
Each of those pages automatically gets a \x[table-of-contents]
* \x[embed-includes] single file output from multiple input files. Includes are parsed smartly, not just source copy pasted, e.g. included headers are shifted from `h1` to `h2` correctly.

On the previous sample filesystem, it would produce a single output file `index.html` which would contain a header structure like:
``
= My website

== h2

=== Not readme

==== Not readme h2
``
* supports both local serverless rendering to HTML files for local viewing, and server oriented rendering such as GitHub pages, e.g. \x[internal-cross-reference]{p} automatically get `.html` extension and or not. E.g.:
* locally, a link `\x[not-readme]` would render as `` and `not-readme.bigb` produces `not-readme.html`
* when publishing, `\x[not-readme]` would render as `
` and `not-readme.bigb` also produces `not-readme.html`, which the server converts to just `http://my-website.com/not-readme`
* cross file configuration files to factor out common page parts like headers, footers and other metadata, e.g.:
* `main.liquid.html`: https://github.com/Shopify/liquid[Liquid template] used for all pages, see example at: \x[play-with-the-template]{full}
* `main.scss`: CSS stylesheet generated from https://sass-lang.com/[SASS] input, see example at: \x[play-with-the-template]{full}
* `ourbigbook.tex`: global LaTeX math definitions, e.g.:
``
\newcommand{\abs}[1]{\left|#1\right|}
``
and then you can use:
``
$\abs{x}$
``
in any .bigb file of the project.
* \x[ourbigbook-json]: per repository configuration options
* \x[table-of-contents] that crosses input files via includes. E.g. in:

README.bigb
``
= My website

== h2

\Include[not-readme]
``
not-readme.bigb
``
= Not readme

== Not readme h2
``
the table of contents for `index.html` also contains the headers for `not-readme.bigb` producing:
* My website
* h2
* Not readme
* Not readme h2
This means that you can split large \x[h-splitdefault-argument][splitDefault] input files if rendering starts to slow you down, and things will still render exactly the same.
* check that local files and images linked to actually exist: \x[a-check-argument]. E.g.:
``
\a[i-don-exist.txt]
``
would lead to a build error.
* associate headers to files with the \x[h-file-argument] e.g.:
``
Here's an example of a nice image: \x[file/path/to/my/image.png].

= path/to/my/image.png
{file}

This image was taken when I was on vacation!
``
would automatically add a preview of the image on the output.
* advanced header/ID related features:
* \x[id-based-header-levels]:
``
= Furry animal

I like \x[furry-animal]{p}, especially my cat, here is his photo: \x[image-my-cat].

== Cat

\Image[My_cat.jpg]
{title=My cat.}
``
* \x[scope]{p} either with directories or with within a single file:
``
See the important conclusion of my experiment: \x[report-of-my-experiment/conclusion]

= Report of my experiment
{scope}

== Introduction

== Middle

== Conclusion
``
* \x[cross-reference-title-inflection] for capitalization and pluralization, e.g.;
``
= Dog

== Snoopy
{c}

\x[dog]{c}{p} are fun. But the \x[dog] I like the most is \x[snoopy]!
``
would render:
* `\x[dog]{c}{p}` as `Dogs`: capitalized because of `{c}` and pluralized because of `{p}`
* `\x[dog]` as `dogs`: auto lowercased because its header `= Dog` does not have `{c}`
* `\x[snoopy]` as `Snoopy`: title capitalization kept to upper case due to `{c}` on the header `== Snoopy`
* \x[synonym]{p}, e.g.:
``
= User interface

= UI
{c}
{synonym}
{title2}

\x[user-interface]{c} is too long, I just say \x[ui].
``
would render something like:
``
User interface is too long, I just say UI
``
Furthermore, this also generates a output file:
``
ui.html
``
which redirects to the ain `user-interface.html`, so it serves as a way to have backward compatibility on page renames.

And the `title2` makes it appears on the main title under parenthesis, something like:
``

User interface (UI)


``
* \x[h-disambiguate-argument][header disambiguation], e.g.:
``
My favorite fruits are \x[apple-fruit]{p}!

My favorite least favorite brand is is \x[apple-company]! \x[apple] computers are too expensive.

== Apple
{disambiguate=fruit}

== Apple
{c}
{disambiguate=company}

= Apple
{c}
{synonym}
``
which renders something like:
* `\x[apple-fruit]{p}`: `apples`
* `\x[apple-company]`: `Apple`
* `\x[apple]`: also `Apple` because of the synonym
* `== Apple\n{disambiguate=fruit}`: `

Apple (fruit)

`
* `== Apple\n{disambiguate=company}`: `

Apple (company)

`
* tags are regular headers: \x[h-child-argument], \x[x-child-argument]
``
= Animal

== Dog
{tag=domestic}
{tag=cute}

== Cat
{tag=domestic}
{tag=cute}

== Bat
{tag=flying}

= Flying

= Cute

= Domestic
``
* \x[unlimited-header-levels], levels higher than 6 are rendered in HTML as an appropriately styled `div`s with an ID:
``
= h1

== h2

=== h3

==== h4

===== h5

====== h6

======= h7

======== h8
``
* generate lists of \x[incoming-links] between internal headers: it shows every internal link coming into the current page
* is written in JavaScript and therefore runs natively on the browser to allow live previews as shown at: https://cirosantilli.com/ourbigbook/editor[]
* helps you with the publishing:
* `ourbigbook --publish` publishes in a single command to the configured target (default GitHub pages): \x[publish]{full}
* OurBigBook tries to deal with media such as images and video intelligently for you, e.g.: \x[where-to-store-images]{full}. E.g. you can keep media in a separate media repository, `my-media-repository`, and then by configuring on \x[ourbigbook-json]:
``
"media-providers": {
"github": {
"default-for": ["image", "video"],
"path": "media",
"remote": "yourname/myproject-media"
}
}
``
you can use images in that repository with:
``
\Image[My_image_basename.jpg]
``
instead of:
``
\Image[https://raw.githubusercontent.com/cirosantilli/myproject--media/master/My_image_basename.jpg]
``
* `inotifywait` watch and automatically rebuild with \x[watch]:
``
ourbigbook --watch input-file.bigb
``

= Quick start
{parent=ourbigbook}

= Play with the template
{parent=quick-start}

Learn the syntax basics in 5 minutes: https://cirosantilli.com/ourbigbook/editor[].

Play with https://github.com/cirosantilli/ourbigbook-template[a OurBigBook template] locally:
``
git clone https://github.com/cirosantilli/ourbigbook-template
cd ourbigbook-template
npm install
npx ourbigbook .
firefox index.html
``
That template can be seen rendered live at: http://cirosantilli.com/ourbigbook-generate-multifile/ Other templates are documented at: \x[generate].

To \x[publish-to-github-pages] on your repository you can just fork the repository https://github.com/cirosantilli/ourbigbook-template to your own https://github.com/johndoe/ourbigbook-template and then:
``
git remote set-url origin git@github.com:johndoe/ourbigbook-template.git
npx ourbigbook --publish
``
and it should now be visible at: https://johndoe.github.io/ourbigbook-template

Then, every time you make a change you can publish the new version with:
``
git add .
git commit --message 'hacked stuff'
ourbigbook --publish .
``
or equivalently with the \x[publish-commit] shortcut:
``
ourbigbook --publish-commit 'hacked stuff'
``

If you want to publish to your root page https://johndoe.github.io instead of https://johndoe.github.io/ourbigbook-template you need to rename the `master` branch to `dev` as mentioned at \x[publish-to-github-pages-root-page]:
``
git remote set-url origin git@github.com:johndoe/johndoe.github.io.git

# Rename master to dev, and delete the old master.
git checkout -b dev
git push origin dev:dev
git branch -D master
git push --delete origin master

npx ourbigbook --publish
``

The following files of the template control the global style of the output, and you are free to edit them:
* `main.liquid.html`: global HTML template in https://shopify.github.io/liquid/[Liquid format]. Available variables are documented at \x[template], and it is being selected in that repository with :
``
"template": "main.liquid.html"
``
in the \x[ourbigbook-json] configuration file.
* `main.scss`: https://sass-lang.com/[Sass] file that gets converted to raw CSS `main.css` by `npx ourbigbook .`.

Sass is just much more convenient to write than raw CSS.

That file gets included into the global HTML template inside `main.liquid.html` at:
``

``

= Important command line options
{parent=quick-start}

When you run:
``
npx ourbigbook .
``
it converts all files in the current directory separately, e.g.:
* `README.bigb` to `index.html`, since `README` is a magic name that we want to show on the root URL
* `not-readme.bigb` to `not-readme.html`, as this one is a regular name unlike `README`
* `main.scss` to `main.css`

If one of the input files starts getting too large, usually the toplevel `README.bigb` in which you dump everything by default like Ciro does, you can speed up development and just compile files individually with either:
``
npx ourbigbook README.bigb
npx ourbigbook not-readme.bigb
``
Note however that when those individual files have a \x[internal-cross-file-reference] to something defined in `not-readme.bigb`, e.g. via `\x[h2-in-not-the-readme]`, then you must first do a first pass once with:
``
npx ourbigbook .
``
to parse all files and extract all necessary IDs to the \x[id-database]. That would be optimized slightly wit the \x[no-render] command line option:
``
npx ourbigbook --no-render .
``
to only extract the IDs but not render, which speeds things up considerably

When dealing with large files, you might also be interested in the following amazing options:
* \x[split-headers]
* \x[h-splitdefault-argument]

To produce a single standalone output file that contains everything in a directory run:
``
npx ourbigbook --embed-resources --embed-includes README.bigb
xdg-open index.html
``
You can now just give `index.html` to any reader and they should be able to view it offline without installing anything. The flags are:
* \x[embed-includes]: without this, `\Include[not-readme]` shows as a link to the file `not-readme.html` which comes from `not-readme.bigb` With the flag, `not-readme.bigb` output gets embedded into the output `index.html` directly
* \x[embed-resources]: by default, we link to CSS and JavaScript that lives inside `node_modules`. With this flag, that CSS and JavaScript is copied inline into the document instead. One day we will try to handle \x[image]{p} that way as well

= Useless knowledge
{parent=quick-start}

Install the NPM package globally and use it from the command line for a quick conversion:
``
npm install -g ourbigbook
printf 'ab\ncd\n' | ourbigbook --body-only
``
or to a file:
``
printf 'ab\ncd\n' | ourbigbook > tmp.html
``
You almost never want to do this except when \x[developing-ourbigbook], as it won't be clear what version of `ourbigbook` the document should be compiled with. Just be a good infant and use OurBigBook \x[play-with-the-template][with the template] that contains a `package.json` via `npx`, OK?

Furthermore, the default install of Chromium on Ubuntu 21.04 uses Snap and blocks access to dotfiles. For example, in a sane NVM install, our global CSS would live under `/home/ciro/.nvm/versions/node/v14.17.0/lib/node_modules/ourbigbook/dist/ourbigbook.css`, which gets blocked because of the `.nvm` part:
* https://forum.snapcraft.io/t/dot-files/7062
* https://bugs.launchpad.net/snapd/+bug/1607067
* https://superuser.com/questions/1546550/chromium-81-wont-display-dotfiles-anymore
* https://askubuntu.com/questions/1184357/why-cant-chromium-suddenly-access-any-partition-except-for-home
* https://askubuntu.com/questions/1214346/as-a-user-is-there-any-way-to-change-the-confinement-of-a-snap-package
One workaround is to use \x[embed-resources], but this of course generates larger outputs.

To run master globally from source for development see: \x[run-ourbigbook-master]{full}. This one actually works despite the dotfile thing since your development path is normally outside of dotfiles.

Try out the JavaScript API with \a[lib_hello.js]:
``
npm install ourbigbook
./lib_hello.js
``

= Design goals
{parent=ourbigbook}

OurBigBook is designed entirely to allow writing complex professional HTML and PDF scientific books, blogs, articles and encyclopedias.

OurBigBook aims to be the ultimate \x[latex-output-format][LaTeX] "killer", allowing books to be finally published as either HTML or PDF painlessly (LaTeX being only a backend to PDF generation).

It aims to be \x[features][more powerful] and \x[saner] and than Markdown and Asciidoctor.

= Saner
{parent=design-goals}

Originally, OurBigBook was is meant to be both saner and more powerful than Markdown and Asciidoctor.

But alas, as Ciro started implementing and using it, he started to bring some Markdown \x[insane-macro-shortcuts][insanity he missed back in].

And so this "degraded" slightly into a language slightly saner than Asciidoctor but with an amazing Node.js implementation that makes it better for book writing and website publishing.

Notably, we hope that our escaping will be a bit saner backslash escapes everything instead of Asciidoctor's "different escapes for every case" approach: https://github.com/asciidoctor/asciidoctor/issues/901

But hopefully, having starting from a saner point will still produce a saner end result, e.g. there are sane constructs for every insane one.

It is intended that this will be an acceptable downside as OurBigBook will be used primarily large complex content such as books rather than forum posts, and will therefore primarily written either:
* in text editors locally, where users have more features than in random browser textareas
* in a dedicated website that will revolutionize education, and therefore have a good JavaScript editing interface: https://github.com/cirosantilli/write-free-science-books-to-get-famous-website

For example, originally OurBigBook had exactly five magic characters, with similar functions as in LaTeX:
* `\` backslash to start a macro, like LaTeX
* `{` and `}`: left and right square brackets to delimit \x[positional-vs-named-arguments][optional macro arguments]
* `[` and `]`: left and right curly braces bracket to start an optional arguments
and double blank newlines for \x[paragraph]{p} if you are pedantic, but this later degenerated into many more with \x[insane-macro-shortcuts].

We would like to have only square brackets for both optional and mandatory to have even less magic characters, but that would make the language difficult to parse for computer and humans. LaTeX was right for once!

This produces a very regular syntax that is easy to learn, including doing:
* arbitrary nesting of elements
* adding arbitrary properties to elements

This sanity also makes the end tail learning curve of the endless edge cases found in Markdown and Asciidoctor disappear.

The language is designed to be philosophically isomorphic to HTML to:
* further reduce the learning curve
* ensure that most of HTML constructs can be reached, including arbitrary nesting

More precisely:
* macro names map to tag names, e.g.: `\\a` to `* one of the arguments of macros, maps to the content of the HTML element, and the others map to attributes.

E.g., in a link:
``\a[http://example.com][Link text\]``
the first macro argument:
``http://example.com``
maps to the `href` of ` ``Link text``
maps to the internal content of `Link text<>`.

= More powerful
{parent=design-goals}

The \x[saner][high sanity of OurBigBook], also makes creating new macro extensions extremely easy and intuitive.

All built-in language features use the exact same API as new extensions, which ensures that the extension API is sane forever.

Markdown is clearly missing many key features such as block attributes and \x[internal-cross-reference]{p}, and has no standardized extension mechanism.

The "more powerful than Asciidoctor" part is only partially true, since Asciidoctor is very featureful can do basically anything through extensions.

The difference is mostly that OurBigBook is completely and entirely focused on making amazing scientific books, and so will have key features for that application out-of-the box, notably:
* amazing header/ToC/ID features including proper error reports: never have a internal broken link or duplicate ID again
* \x[mathematics][server side pre-rendered maths with KaTeX]: all divs and spans are ready, browser only applies CSS, no JavaScript gets executed
* \x[publish]: we take care of website publishing for you out-of-the-box, no need to integrate into an external project like Jekyll
* \x[split-headers]:
* https://github.com/asciidoctor/asciidoctor/issues/626 feature request
* https://github.com/owenh000/asciidoctor-multipage third party plugin that does it
and we feel that some of those features have required specialized code that could not be easily implemented as a standalone macro.

Another advantage over Asciidoctor is that the reference implementation of OurBigBook is in JavaScript, and can therefore be used on browser live preview out of the box. Asciidoctor does Transpile to JS with https://github.com/opal/opal[Opal], but who wants to deal with that layer of complexity?

= Related projects
{parent=design-goals}

Static wiki generators: this is perhaps the best way of classifying this project :-)
* https://github.com/gollum/gollum[]: already has a local server editor! But no WYSIWYG nor live preview. Git integration by default, so when you save on the UI already generates a Git commit. We could achieve that with: https://github.com/isomorphic-git/isomorphic-git[], would be really nice. Does not appear to have built-in static generation:
* https://stackoverflow.com/questions/7210391/have-anyone-use-gollum-site-to-generete-markdown-wikis-and-host-it-on-heroku
* https://github.com/dreverri/gollum-site
Does not appear to check that any links are correct.
* https://github.com/wcchin/markypydia
* https://obsidian.md/ closed source, Markdown with \x[internal-cross-file-reference] + a SaaS. Appears to require payment for any publishing. 28k followers 2021: https://twitter.com/obsdmd[]. Founders are likely Canadians of Asian descent from Waterloo University: https://www.linkedin.com/in/lishid/ | https://www.linkedin.com/in/ericaxu/ also working in parallel on https://dynalist.io/ 2020 review at: https://www.youtube.com/watch?v=aK2fOQRNSxc Has offline editor with side-by-side preview. Compares with https://roamresearch.com/[Roam] and https://roamresearch.com/[Notion], but can't find any public publishing on those, seem to be enterprise only things.

Static book generators:
* https://github.com/rstudio/bookdown[], https://bookdown.org/[]. Very similar feature set to what we want!!! Transpiles to markdown, and then goes through Pandoc: https://bookdown.org/yihui/bookdown/pandoc.html[], thus will never run on browser without huge translation layers. But does have an obscene amount of output formats however.
* https://gohugo.io/[Hugo]. Pretty good, similar feature set to ours. But Go based, so hard on browser, and adds adhoc features on top of markdown once again
* https://en.wikipedia.org/wiki/Personal_wiki
* https://github.com/vimwiki/vimwiki
* https://github.com/hplgit/doconce
* https://www.gwern.net/About#source is pretty interesting, uses https://github.com/jaspervdj/Hakyll/ + some custom stuff.
* https://github.com/JerrySievert/bookmarkdown
* https://www.gitbook.com/
* https://github.com/rust-lang/mdBook[]. Impressive integrated search feature. Like Gitbook but implemented in Rust.
* https://github.com/facebook/docusaurus React + markdown based, written in TypeScript. So how can it be build fast? Gotta benchmark.

Less related but of interest, similar philosophy to what Ciro wants, but no explicitly reusable system:
* http://www.uprtcl.io/
* https://libretexts.org
* https://physics.info/
* https://hypertextbook.com/
* https://tutorial.math.lamar.edu/

= Motivation
{parent=design-goals}

Ciro Santilli developed OurBigBook to perfectly satisfy his writing style, which is basically "create one humongous document where you document everything you know about a subject so everyone can understand it, and just keep adding to it".

https://cirosantilli.com[] is the first major document that he has created in OurBigBook.

He decided to finally create this new system after having repeatedly facing limitations of Asciidoctor which were ignored/wontfixed upstream, because Ciro's writing style is not as common/targeted by Asciidoctor.

Following large documents Ciro worked extensively on:
* https://github.com/cirosantilli/china-dictatorship
* https://github.com/cirosantilli/linux-kernel-module-cheat
made the limitations of Asciidoctor clear to Ciro, and were major motivation in this work.

The key limitations have repeatedly annoyed Ciro were:
* cannot go over header level 6, addressed at: \x[unlimited-header-levels]
* the need for \x[split-headers] to avoid one too large HTML output that will never get indexed properly by search engines, and takes a few seconds to load on any browser, which is unacceptable user experience

= OurBigBook Markup
{c}
{parent=ourbigbook}

OurBigBook Markup is the markup language used in the \x[ourbigbook] project.

It works both on the \x[ourbigbook-web] dynamic website, and on \x[ourbigbook-cli] static websites from the command line.

= Macro
{parent=ourbigbook-markup}

This section documents all OurBigBook macros.

Macros are magic commands that do cool stuff, e.g. `\Image` to create an image.

The most common macros also have \x[insane-macro-shortcuts] to keep the syntax shorter.

The general macro syntax is described at \x[ourbigbook-markup-syntax]{full}.

= Link
{parent=macro}

= `\a`
{synonym}
{title2}

\x[insane-macro-shortcuts][Insane] autolink (link text is the same as the link):
\OurbigbookExample[[
The website http://example.com is cool. See also:

\Q[http://example.com/2]
]]
Exact parsing rules described at: \x[insane-link-parsing-rules]{full}.

Equivalent sane version:
\OurbigbookExample[[[
The website \a[http://example.com] is cool.

\Q[\a[http://example.com/2]]
]]]

Insane link with custom text:
\OurbigbookExample[[
The website http://example.com[example.com] is cool.
]]
Equivalent sane version:
\OurbigbookExample[[
The website \a[http://example.com][example.com] is cool.
]]
If the custom text is empty, an autolink is generated. This is often useful if you want your link to be followed by punctuation:
\OurbigbookExample[[
The website is really cool: http://example.com[].
]]
This could also be achieved with the sane syntax of course, but this pattern saves a tiny bit of typing.

Link with multiple paragraphs inside it:
\OurbigbookExample[[
\a[http://example.com][Multiple

paragraphs]
]]

= `\a` `check` argument
{parent=link}

If `{check=0}` is given, this disables the local file existence check that is done by default for \x[relative-link]{p}.

If `check` is not given explicitly, OurBigBook does the check by default if the link is not a \x[url-with-protocol] For example, the following are not checked:
* `http://cirosantilli.com`
* `https://cirosantilli.com`
* `file:///etc/fstab`
* `ftp://cirosantilli.com`
and the following are:
* `index.js`
* `../index.js`
* `path/to/index.js`
* `/path/to/index.js`. Since it stats with a `/`, this path has to exist relative to \x[project-toplevel-directory], not relative to the current `.bigb` source.
* `//example.com/path/to/index.js`. This gets treated the same as `/example.com/path/to/index.js`.

For example, it is often the case in computer programming tutorials that we want to refer to source files in the current directory, so you could have in your `README.bigb`:
``
See this awesome source file: \a[index.js]
``
and then if `index.js` does not exist in the project, compilation leads to an error.

This check is important because as you start documenting several source files, it is almost inevitable getting wrong paths due to renames or typos without this type of error checking

The most common use case for disabling checks is as follows.

https://github.com/cirosantilli/cirosantilli.github.io/blob/da296c3c933704484d5cd1a42754f60ec00f672b/README.bigb was rendered at https://cirosantilli.com[], and contains links to https://cirosantilli.com/markdown-style-guide[], whose source lives in a separate non-OurBigBook repository: https://github.com/cirosantilli/markdown-style-guide/

Therefore, if we did from `README.bigb`:
``
See this awesome style guide: \a[markdown-style-guide]
``
we do not want OurBigBook do check that the file `markdown-style-guide` exists in the local filesystem.

For this reason, we have instead to write:
``
See this awesome style guide: \a[markdown-style-guide]{check=0}
``

The general lesson is clear: in a server, paths could be re-routed to anything, including content that lies outside of a OurBigBook project.

= `\a` `href` argument
{parent=link}

The link target, e.g. in:
``
\a[http://example.com]
``
`href` equals `http://example.com`.

Important behaviours associated with this property for local links:
* they are checked for existence in the local filesystem: \x[a-check-argument]
* they are modified as per \x[relative-link]{full} to account for \x[scope]{p} with \x[split-headers]

= `\a` `ref` argument
{parent=link}

Analogous to the \x[x-ref-argument], e.g.:
\OurbigbookExample[[
Trump said this and that.https://en.wikipedia.org/wiki/Donald_Trump_Access_Hollywood_tape#Trump's_responses{ref}https://web.archive.org/web/20161007210105/https://www.donaldjtrump.com/press-releases/statement-from-donald-j.-trump{ref} Then he said that and this.https://en.wikipedia.org/wiki/Donald_Trump_Access_Hollywood_tape#Trump's_responses{ref}https://web.archive.org/web/20161007210105/https://www.donaldjtrump.com/press-releases/statement-from-donald-j.-trump{ref}
]]

= `\a` `relative` argument
{parent=link}

If given, this \x[boolean-argument] forces a given link to be a \x[relative-link] or not.

Otherwise, the link is automatically guessed based on the address given as explained at \x[relative-link]{full}.

= Relative link
{parent=a-relative-argument}

A relative link is a link that points to a resource that will be present a final URL relative to the input `.bigb` file.

For example, it is often the case in computer programming tutorials that we want to refer to source files in the current directory.

So from our `README.bigb`, we could want to write something like:
\OurbigbookExample[[
Have a look at this amazing source file: \a[index.js].
]]
and here `\a[ourbigbook]` is a relative link.

A non-relative link is something like:
\OurbigbookExample[[
This is great website: https://cirosantilli.com
]]
which points to an absolute URL.

A link being relative has the following effects
* the correct relative path to the file is used when using nested \x[scope]{p} with \x[split-headers]. For example, if we have:
``
= h1

== h2
{scope}

=== h3

\a[index.js]
``
then in split header mode, `h3` will be rendered to `h2/h3.html`.

Therefore, if we didn't do anything about it, the link to `index.js` would render as `href="index.js"` and thus point to `h2/index.js` instead of the correct `index.js`.

Instead, OurBigBook automatically converts it to the correct `href="../index.js"`

OurBigBook considers a link relative by default if:
* it is not a \x[url-with-protocol]
* it does not start with a slash `/`

Therefore, the following are not relative links by default:
* `http://cirosantilli.com`
* `https://cirosantilli.com`
* `file:///etc/fstab`
* `ftp://cirosantilli.com`
* `/path/to/index.js`
* `//example.com/path/to/index.js`
and the following are:
* `index.js`
* `../index.js`
* `path/to/index.js`

Implemented at: https://github.com/cirosantilli/ourbigbook/issues/87[].

= URL with protocol
{c}
{parent=relative-link}

A URL with protocol is a URL that matches the regular expression `^[a-zA-Z]+://`. The following are examples of URLs with protocol:
* `http://cirosantilli.com`
* `https://cirosantilli.com`
* `file:///etc/fstab`
* `ftp://cirosantilli.com`

The following aren't:
* `index.js`
* `../index.js`
* `path/to/index.js`
* `/path/to/index.js`
* `//example.com/path/to/index.js`. This one is a bit tricky. Web browsers would consider this as a https://stackoverflow.com/questions/28446314/why-use-protocol-relative-urls-at-all[protocol-relative URL], which technically implies a protocol, although that protocol would be different depending how you are viewing the file, e.g. locally through `file://` vs on a with website `https://`.

For simplicity's sake, we just consider it as a URL without protocol.

= Insane link parsing rules
{parent=link}

Insane start at any of the recognized protocols are the ones shown at: \x[known-url-protocols]{full}.
* `http://`
* `https://`
absolutely anywhere if not escaped, e.g.:
``
ahttp://example.com
``
renders something like:
``
a
``
To prevent expansion, you have to escape the protocol with a backslash `\\`, e.g.:
``
\http://example.com
``
Empty domains like:
``
http://
``
don't becomes links however. But this one does:
``
http://a
``

Insane links end when either the end of the document or one of the following characters is found:
* space ` `
* newline `\n`
* open or close square bracket `[` or `]`
* open or close curly braces `{` or `}`

As a consequence, to have an insane link followed immediately by a punctuation like a period you should use an empty argument as in:
\OurbigbookExample[[
Check out this website: http://example.com[].
]]
otherwise the punctuation will go in it. Another common use case is:
\OurbigbookExample[[
As mentioned on the tutorial (http://example.com[see this link]).
]]

If you want your link to include one of the terminating characters, e.g. `]`, all characters can be escaped with a backslash, e.g.:
\OurbigbookExample[[
Hello http://example.com/\]a\}b\\c\ d world.
]]

Note that the `http://example.com` inside `\a[http://example.com]` only works because we do some post-processing magic that prevents its expansion, otherwise the link would expand twice:
\OurbigbookExample[[
\P[http://example.com]

\a[http://example.com]
]]
This magic can be observed with \x[help-macros] by seeing that the `href` argument of the `a` macro has the property:
``
"elide_link_only": true,
``

= Bold
{parent=macro}
{title2=`\b`}

\OurbigbookExample[[
Some \b[bold] text.
]]

= Line break
{parent=macro}
{title2=`\br`}

There is basically one application for this: poetry, which would be too ugly with \x[code-block] due to fixed width font:
\OurbigbookExample[[
Paragraph 1 Line 1\br
Paragraph 1 Line 2\br

Paragraph 2 Line 1\br
Paragraph 2 Line 2\br
]]

= Code block
{parent=macro}
{title2=\c[[``]], \c[[`]], `\C`, `\c`}

Inline code (code that should appear in the middle of a paragraph rather than on its own line) is done with a single backtick (\c[[`]]) \x[insane-macro-shortcuts][insane macro shortcut]:
\OurbigbookExample[[
My inline `x = 'hello\n'` is awesome.
]]
and block code (code that should appear on their own line) is done with two or more backticks (\c[[``]]):
\OurbigbookExample[[
``
f() {
return 'hello\n';
}
``
]]

The sane version of inline code is a lower case `c`:
\OurbigbookExample[[[
My inline \c[[x = 'hello\n']] is awesome.
]]]
and the sane version of block math is with an upper case `C`:
\OurbigbookExample[[[
\C[[
f() {
return 'hello\n';
}
]]
]]]

The capital vs lower case theme is also used in other elements, see: \x[block-vs-inline-macros].

If the content of the sane code block has many characters that you would need to \x[escape-characters][escape], you will often want to use \x[literal-arguments], which work just like the do for any other argument. For example:
\OurbigbookExample[[[[
\C[[[
A paragraph.

\C[[
And now, some long, long code, with lots
of chars that you would need to escape:
\ [ ] { }
]]

A paragraph.
]]]
]]]]
Note that the initial newline is skipped automatically in code blocks, just as for any other element, due to: \x[argument-leading-newline-removal], so you don't have to worry about it.

The distinction between inline `\c` and block `\C` code blocks is needed because in HTML, https://stackoverflow.com/questions/5371787/can-i-have-a-pre-tag-inside-a-p-tag-in-tumblr/58603596#58603596[`pre` cannot go inside `P`].

We could have chosen to do some magic to differentiate between them, e.g. checking if the block is the only element in a paragraph, but we decided not to do that to keep the language saner.

And now a code block outside of \x[ourbigbookexample] to test how it looks directly under \x[toplevel]:

``
Hello

Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello
HelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHello
Hello
``

And nos a very long inline code: `Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello`

\Comment[[[[
TODO implement.
We can have cross references to code blocks as for other elements such as \x[image]{p}:
\OurbigbookExample[[[
See this awesome code \x[my-code]:
``
ab
cd
``
{id=my-code}
]]]
]]]]

Block code can have a title, e.g. see this one: \x[code-my-nice-code]{full}:
\OurbigbookExample[[
``
ab
cd
``
{id=code-my-nice-code}
{title=My nice code block.}
]]

= `\OurbigbookExample`
{parent=macro}

Shows both the OurBigBook code and its rendered output, e.g.:
\OurbigbookExample[[[
\OurbigbookExample[[
Some `ineline` code.
]]
]]]

Its input should be thought of as a literal code string, and it then injects the rendered output in the document.

This macro is used extensively in the OurBigBook documentation.

= Comment
{parent=macro}
{title2=`\Comment`}

The `Comment` and `comment` macros are regular macros that does not produce any output. Capitalization is explained at: \x[block-vs-inline-macros]{full}.

You will therefore mostly want to use it with a \x[literal-arguments][literal argument], which will, as for any other macro, ignore any macros inside of it.
\OurbigbookExample[[[
Before comment.

\Comment[[
Inside comment.
]]

After comment.
]]]

And an inline one:
\OurbigbookExample[[[
My inline \comment[[inside comment]] is awesome.

\comment[[inside comment]] inline at the start.
]]]

= Header
{parent=macro}
{title2=`\H`}

\x[insane-macro-shortcuts][Insane] with `= ` (equal sign space):
``
= My h1

== My h2

=== My h3
``
Insane headers end at the first newline found. They cannot therefore contain raw newline tokens.

Equivalent sane:
``
\H[1][My h1]

\H[2][My h2]

\H[3][My h3]
``

Custom ID for \x[internal-cross-reference]{p} on insane headers:
``
= My h1
{id=h1}

== My h2
{id=h2}

=== My h3
{id=h3}
``

Sane equivalent:
``
\H[1][My h1]{id=h1}

\H[2][My h2]{id=h2}

\H[3][My h3]{id=h3}
``

= Unlimited header levels
{parent=header}

There is no limit to how many levels we can have, for either sane or insane headers!

HTML is randomly limited to `h6`, so OurBigBook just renders higher levels as an `h6` with a `data-level` attribute to indicate the actual level for possible CSS styling:
``
My title

``

The recommended style is to use insane headers up to `h6`, and then move to sane one for higher levels though, otherwise it becomes very hard to count the `=` signs.

To avoid this, we considered making the insane syntax be instead:
``
= 1 My h1
= 2 My h2
= 3 My h3
``
but it just didn't feel as good, and is a bit harder to type than just smashing `=` n times for lower levels, which is the most common use case. So we just copied markdown.

= My h3
{parent=unlimited-header-levels}

= My h4
{parent=my-h3}

= My h5
{parent=my-h4}

= My h6
{parent=my-h5}

= My h7
{parent=my-h6}

= My h8
{parent=my-h7}

= My h9
{parent=my-h8}

= My h10
{parent=my-h9}

= My h11
{parent=my-h10}

= My h12
{parent=my-h11}

= My h13
{parent=my-h12}

= Skipping header levels
{parent=header}

The very first header of a document can be of any level, although we highly recommend your document to start with a `\H[1]`, and to contain exactly just one `\H[1]`, as this has implications such as:
* `\H[1]` is used for the document title: \x[html-document-title]
* `\H[1]` does not show on the \x[table-of-contents]

After the initial header however, you must not skip a header level, e.g. the following would give an error because it skips level 3:
``
= my 1

== my 1

==== my 4
``

= The toplevel header
{parent=header}

If the document has only a single header of the highest level, e.g. like the following has only a single `h2`:
``
== My 2

=== My 3 1

=== My 3 2
``
then this has some magical effects.

= The toplevel header IDs don't show
{parent=the-toplevel-header}

Header IDs won't show for the toplevel level. For example, the headers would render like:
``
My 2

1. My 3 1

2. My 3 2
``
rather than:
``
1. My 2

1.2. My 3 1

1.2. My 3 2
``
This is because in this case, we guess that the `h2` is the toplevel.

= The ID of the first header is derived from the filename
{parent=the-toplevel-header}

TODO: we kind of wanted this to be the ID of the toplevel header instead of the first header, but this would require an extra postprocessing pass (to determine if the first header is toplevel or not), which might affect performance, so we are not doing it right now.

When the OurBigBook input comes from a file (and not e.g. stdin), the default ID of the first header in the document is derived from the basename of the OurBigBook input source file rather than from its title.

This is specially relevant when \x[include][including] other files.

For example, in file named `my-file.bigb` which contains:
``
= Awesome ourbigbook file
]]
``
the ID of the header is `my-file` rather than `awesome-ourbigbook-file`. See also: \x[automatic-id-from-title].

If the file is an \x[index-file] other than \x[the-toplevel-index-file], then the basename of the parent directory is used instead, e.g. the toplevel ID of a file:
``my-subdir/README.bigb``
would be:
``#my-subdir``
rather than:
``#README.bigb``

For the toplevel index file however, the ID is just taken from the header itself as usual. This is done because you often can't general control the directory name of a project.

For example, a \x[publish-to-github-pages][GitHub pages] root directory must be named as `.github.io`. And users may need to rename directories to avoid naming conflicts.

As a consequence of this, the toplevel index file cannot \x[include][be included in other files].

= `\H` arguments
{parent=header}

= `\H` `c` argument
{parent=h-arguments}

If given, makes the header capitalized by default on \x[internal-cross-file-reference]{p}.

More details at: \x[cross-reference-title-inflection]{full}.

= `\H` `child` argument
{parent=h-arguments}

This \x[multiple-argument] marks given IDs as being children of the current page.

The effect is the same as adding the \x[x-child-argument] argument to an under the header. Notably, such marked target IDs will show up on the \x[tagged] autogenerated \x[header-metadata-section].

Example:
``
= Animal

== Mammal

=== Bat

=== Cat

== Wasp

== Flying animal
{child=bat}
{child=wasp}

\x[bat]

\x[wasp]
``
renders exactly as:
``
= Animal

== Mammal

=== Bat

=== Cat

== Wasp

== Flying animal

\x[bat]{child}

\x[wasp]{child}
``

The header `child` syntax is generally preferred because at some point while editing the content of the header, you might accidentally remove mentions to e.g. `\x[bat]{child}`, and then the relationship would be lost.

The \x[h-tag-argument] does the same as the \x[x-child-argument] but in the opposite direction.

= `\H` `disambiguate` argument
{parent=h-arguments}

Sometimes the short version of a name is ambiguous, and you need to add some extra text to make both its title and ID unique.

For example, the word "Python" could either refer to:
* the programming language: https://en.wikipedia.org/wiki/Python_(programming_language)
* the genus of snakes: https://en.wikipedia.org/wiki/Python_(genus)

The `disambiguate` \x[positional-vs-named-arguments][name argument], which is automatically defined for all macros, helps you deal more neatly with such problems.

Have a look at this example:
``
My favorite snakes are \x[python-genus]{p}!

My favorite programming language is \x[python-programming-language]!

\x[python-genus]{full}

\x[python-programming-language]{full}

== Python
{disambiguate=genus}

== Python
{c}
{disambiguate=programming language}
{title2=.py}
{wiki}
``
which renders as:
\Q[
My favorite snakes are \x[python-genus]{p}!

My favorite programming language is \x[python-programming-language]!

\x[python-genus]{full}

\x[python-programming-language]{full}

= Python
{disambiguate=genus}
{parent=h-disambiguate-argument}

= Python
{c}
{disambiguate=programming language}
{parent=h-disambiguate-argument}
{title2=.py}
{wiki}
]
from which we observe how `disambiguate`:
* gets added to the ID after conversion following the same rules as \x[automatic-id-from-title]
* shows up on the header between parenthesis, much like Wikipedia, as well as in \x[x-full-argument][`full` cross references]
* does not show up on non-`full` references. This makes it much more likely that you will be able to reuse the title automatically on a cross reference without `content`: we wouldn't want to say "My favorite programming language is Python (programming language)" all the time, would we?
* gets added to the default \x[h-wiki-argument] inside parenthesis, following Wikipedia convention, therefore increasing the likelihood that you will be able to go with the default Wikipedia value

Besides disambiguating headers, the `disambiguate` argument has a second related application: disambiguating IDs of images. For example:
\OurbigbookExample[[
\x[image-the-title-of-my-disambiguate-image]{full=0}

\x[image-the-title-of-my-disambiguate-image-2]{full=0}

\x[image-the-title-of-my-disambiguate-image]{full}

\x[image-the-title-of-my-disambiguate-image-2]{full}

\Image[Tank_man_standing_in_front_of_some_tanks.jpg]
{title=The title of my disambiguate image.}

\Image[Tank_man_standing_in_front_of_some_tanks.jpg]
{title=The title of my disambiguate image.}
{disambiguate=2}
]]
Note that unlike for headers, `disambiguate` does not appear on the title of images at all. It serves only to create an unique ID that can be later referred to. Headers are actually the only case where `disambiguate` shows up on the visible rendered output. We intend on making this application obsolete however with:

This use case is even more useful when `title-from-src` is enable by default for the \x[ourbigbook-json/media-providers] entry, so you don't have to repeat titles several times over and over.

= `\H` `file` argument
{parent=h-arguments}

If given, the current section contains metadata about file or other resource with the given URL.

If empty, the URl of the file is extracted directly from the header. Otherwise, the given URL is used.

for example:
``
The file \x[file/path/to/myfile.c] is very useful.

= path/to/myfile.c
{file}

An explanation of what this file is about.
``
renders the same as:
``
The file \x[file/path/to/myfile.c] is very useful.

= path/to/myfile.c
{file}
{id=file/path/to/myfile.c}

An explanation of what this file is about.

\a[path/to/myfile.c][View file]
``
so note how:
* \x[automatic-id-from-title] does not normalize the path, e.g. it does not convert `/` to `-`.

Also, a `file/` prefix is automatically added to the ID. This is needed with \x[split-headers] to avoid a collision between:
* `path/to/myfile.c`: the actual file
* `file/path/to/myfile.c`: the metadata about that file. Note that locally the `.html` extension is added as in `file/path/to/myfile.c.html` which avoids the collision. But on a server deployment, the `.html` is not present, and there would be a conflict if we didn't add that `file/` prefix.
* a link to the is added automatically, since users won't be able to click it from the header, as clicking on the header will just link to the header itself
* a preview is added. The type of preview is chosen as follows:
* if the URL has an image extension, do an \x[image] preview
* otherwise if the URL has a video extension, or is a YouTube URL, do a \x[video] preview
* otherwise, don't show a preview, as we don't know anything sensible to show

In some cases however, especially when dealing with external URLs, we might want to have a more human readable title with a `file` specified as in:
``
The video \x[tank-man-by-cnn-1989] is very useful.

= Tank Man by CNN (1989)
{file=https://www.youtube.com/watch?v=YeFzeNAHEhU}

An explanation of what this video is about.
``
which renders something like:
``
The video \x[tank-man-by-cnn-1989] is very useful.

= Tank Man by CNN (1989)

\a[https://www.youtube.com/watch?v=YeFzeNAHEhU][View file]

An explanation of what this video is about.

\Video[https://www.youtube.com/watch?v=YeFzeNAHEhU]
``

= `\H` `file` argument demo
{parent=h-file-argument}

= Tank_man_standing_in_front_of_some_tanks.jpg
{file}
{parent=h-file-argument-demo}

An explanation of what this video is about.

= Tank Man by CNN (1989)
{file=https://www.youtube.com/watch?v=YeFzeNAHEhU}
{parent=h-file-argument-demo}

An explanation of what this video is about.

= `\H` `numbered` argument
{c}
{parent=h-arguments}

This \x[boolean-argument] determines whether renderings of a header will have section numbers or not. This affects all of:
* \x[header]{p} themselves
* \x[table-of-contents] links
* \x[internal-cross-reference]{p} with the \x[x-full-argument]
This option can be set by default for all files with:

By default, headers are numbered as in a book, e.g.:
``
= h1

== h2

=== h3

==== h4
``
renders something like:
``
= h1

Table of contents
* 1. h2
* 1.1. h3
* 1.1.1. h4

== 1. h2

=== 1.1. h3

==== 1.1.1. h4
``

However, for documents with a very large number of sections, or \x[unlimited-header-levels][deeply nested headers] those numbers start to be more noise than anything else, especially in the table of contents and you are better off just referring to IDs. E.g. imagine:
``
1.3.1.4.5.1345.3.2.1. Some deep level
``

When documents reach this type of scope, you can disable numbering with the `numbered` option.

This option can be set on any header, and it is inherited by all descendants.

The option only affects descendants.

E.g., if in the above example turn numbering off at `h2`:
``
= h1

== h2
{numbered=0}

=== h3

==== h4
``
then it renders something like:
``
= h1

Table of contents
* 1. h2
* h3
* h4

== 1. h2

=== h3

==== h4
``

The more common usage pattern to disable it on toplevel and enable it only for specific "tutorial-like sections". An example can be seen at:
* https://cirosantilli.com/[]: huge toplevel wiki, for which we don't want numbers
* https://cirosantilli.com/x86-paging[]: a specific tutorial, for which we want numbers
which is something like:
``
= Huge toplevel wiki
{numbered=0}

== h2

=== A specific tutorial
{numbered}
{scope}

==== h4

===== h5
``
then it renders something like:
``
= Huge toplevel wiki

Table of contents
* h2
* A specific tutorial
* 1. h4
* 1.1. h5

== h2

=== A specific tutorial

==== 1. h4

===== 1.1. h5
``
Note how in this case the number for `h4` is just `1.` rather than `1.1.1.`. We only show numberings relative to the first non-numbered header, because the `1.1.` wouldn't be very meaningful otherwise.

= `\H` `parent` argument
{c}
{parent=h-arguments}

= ID-based header levels
{c}
{synonym}
{title2}

In addition to the basic way of specifying header levels with an explicit level number as mentioned at \x[header]{full}, OurBigBook also supports a more indirect ID-based mechanism with the `parent` argument of the `\H` element.

We hightly recommend using `parent` for all but the most trivial documents.

For example, the following fixed level syntax:
``
= My h1

== My h2 1

== My h2 2

=== My h3 2 1
``
is equivalent to the following ID-based version:
``
= My h1

= My h2 1
{parent=my-h1}

= My h2 2
{parent=my-h1}

= My h3 2 1
{parent=my-h2-h}
``

The main advantages of this syntax are felt when you have a huge document with \x[unlimited-header-levels][very large header depths]. In that case:
* it becomes easy to get levels wrong with so many large level numbers to deal with. It is much harder to get an ID wrong.
* when you want to move headers around to improve organization, things are quite painful without a refactoring tool (which we intend to provide in the \x[browser-editor-with-preview]), as you need to fix up the levels of every single header.

If you are using the ID-based syntax however, you only have to move the chunk of headers, and change the `parent` argument of a single top-level header being moved.

Note that when the `parent=` argument is given, the header level must be `1`, otherwise OurBigBook assumes that something is weird and gives an error. E.g. the following gives an error:
``
= My h1

== My h2
{parent=my-h1}
``
because the second header has level `2` instead of the required `= My h2`.

When \x[scope]{p} are involved, the rules are the same as those of internal reference resolution, including the leading `/` to break out of the scope in case of conflicts.

See also: \x[header-explicit-levels-vs-nesting-design-choice]{full} for further rationale.

= ID-based header levels and scope resolution
{c}
{parent=h-parent-argument}

When mixing both \x[h-parent-argument] and \x[scope]{p}, things get a bit complicated, because when writing or parsing, we have to first determine the parent header before resolving scopes.

As a result, the follow simple rules are used:
* start from the last header of the highest level
* check if the `{parent=XXX}` is a suffix of its ID
* if not, proceed to the next smaller level, and so on, until a suffix is found

Following those rules for example, a file `tmp.bigb`:
``
= h1
{scope}

= h1 1
{parent=h1}
{scope}

= h1 1 1
{parent=h1-1}

= h1 1 2
{parent=h1-1}

= h1 1 3
{parent=h1/h1-1}

= h1 2
{parent=h1}
{scope}

= h1 2 1
{parent=h1-2}
{scope}

= h1 2 1 1
{parent=h1-2/h1-2-1}
``
will lead to the following header tree with \x[log-headers]:
``
= h1 tmp
== h2 1 tmp/h1-1
=== h3 1.1 tmp/h1-1/h1-1-1
=== h3 1.2 tmp/h1-1/h1-1-2
=== h3 1.3 tmp/h1-1/h1-1-3
== h2 2 tmp/h1-2
=== h3 2.1 tmp/h1-2/h1-2-1
==== h4 2.1.1 tmp/h1-2/h1-2-1/h1-2-1-1
``

= Header explicit levels vs nesting design choice
{parent=h-parent-argument}

Arguably, the language would be even saner if we did:
``
\H[My h1][

Paragraph.

\H[My h2][]
]
``
rather than having explicit levels as in `\H[1][My h1]` and so on.

But we chose not to do it like most markups available because it leads to too many nesting levels, and hard to determine where you are without tooling.

Ciro later "invented" (?) \x[h-parent-argument], which he feels reaches the perfect balance between the advantages of those two options.

= `\H` `scope` argument
{parent=h-arguments}

= Scope
{synonym}

In some use cases, the sections under a section describe inseparable parts of something.

For example, when documenting an experiment you executed, you will generally want an "Introduction", then a "Materials" section, and then a "Results" section for every experiment.

On their own, those sections don't make much sense: they are always referred to in the context of the given experiment.

The problem is then how to get unique IDs for those sections.

One solution, would be to manually add the experiment ID as prefix to every subsection, as in:
``
= Experiments

See: \x[full-and-unique-experiment-name/materials]

== Introduction

== Full and unique experiment name

=== Introduction
{id=full-and-unique-experiment-name/introduction}

See our awesome results: \x[full-and-unique-experiment-name/results]

For a more general introduction to all experiments, see: \x[introduction].

=== Materials
{id=full-and-unique-experiment-name/materials}

=== Results
{id=full-and-unique-experiment-name/results}
``

but this would be very tedious.

To keep those IDs shorter, OurBigBook provides the `scope` \x[boolean-argument] property of \x[header]{p}, which works analogously to C++ namespaces with the header IDs.

Using `scope`, the previous example could be written more succinctly as:
``
= Experiments

See: \x[full-and-unique-experiment-name/materials]

== Introduction

== Full and unique experiment name
{scope}

=== Introduction

See our awesome results: \x[results]

For a more general introduction to all experiments, see: \x[/introduction].

=== Materials

=== Results
``

Note how:
* full IDs are automatically prefixed by the parent scopes prefixed and joined with a slash `/`
* we can refer to other IDs withing the current scope without duplicating the scope. E.g. `\x[results]` in the example already refers to the ID `full-and-unique-experiment-name/materials`
* to refer to an ID outside of the scope and avoid name conflicts with IDs inside of the current scope, we start a reference with a slash `/`

So in the example above, `\x[/introduction]` refers to the ID `introduction`, and not `full-and-unique-experiment-name/introduction`.

= `scope` resolution
{parent=h-scope-argument}

When nested scopes are involved, \x[internal-cross-reference]{p} resolution peels off the scopes one by one trying to find the closes match, e.g. the following works as expected:
``
= h1
{scope}

== h2
{scope}

=== h3
{scope}

\x[h2]
``
Here OurBigBook:
* first tries to loop for an `h1/h2/h3/h2`, since `h1/h2/h3` is the current scope, but that ID does not exist
* so it removes the `h3` from the current scope, and looks for `h1/h2/h2`, which is still not found
* then it removes the `h2`, leading to `h1/h2`, and that one is found, and therefore is taken

= Directory-based `scope`
{parent=h-scope-argument}

Putting files in subdirectories of the build has the same effect as adding a \x[scope] to their top level header.

Notably, all headers inside that directory get the directory prepended to their IDs.

The toplevel directory is determined as described at: \x[the-toplevel-index-file].

= Test scope 1
{parent=h-scope-argument}
{scope}

For fun and profit.

= Test scope 2
{parent=test-scope-1}
{scope}

Let's break this local link: \a[ourbigbook].

= Not scoped
{parent=test-scope-2}

= `\H` `scope` argument of toplevel headers
{parent=h-scope-argument}

When \x[the-toplevel-header] is given the `scope` property OurBigBook automatically uses the file path for the scope and heaves fragments untouched.

For example, suppose that file `full-and-unique-experiment-name` contains:
``
= Full and unique experiment name
{scope}

== Introduction

== Materials
``

In this case, multi-file output will generate a file called `full-and-unique-experiment-name.html`, and the URL of the subsections will be just:
* `full-and-unique-experiment-name.html#introduction`
* `full-and-unique-experiment-name.html#materials`
instead of
* `full-and-unique-experiment-name.html#full-and-unique-experiment-name/introduction`
* `full-and-unique-experiment-name.html#full-and-unique-experiment-name/materials`

Some quick interactive cross file link tests:
* \x[not-readme-with-scope]
* \x[not-readme-with-scope/h2]
* \x[not-readme-with-scope/image-my-image]

= `\H` `splitDefault` argument
{parent=h-arguments}

When using \x[split-headers], \x[internal-cross-reference]{p} always point to non-split pages as mentioned at \x[internal-cross-reference-targets-in-split-headers].

If the `splitDefault` \x[boolean-argument] is given however:
* the split header becomes the default, e.g. `index.html` is now the split one, and `nosplit.html` is the non-split one
* the header it is given for, and all of its descendant headers will use the split header as the default internal cross target, unless the header is already rendered in the current page. This does not propagate across \x[include]{p} however.

For example, consider `README.bigb`:
``
= Toplevel
{splitDefault}

\x[h2][toplevel to h2]

\x[notreadme][toplevel to notreadme]

\Include[notreadme]

== h2
``
and `notreadme.bigb`:
``
= Notreadme

\x[h2][notreadme to h2]

\x[notreadme][notreadme to notreadme h2]

== Notreadme h2
``
Then the following links would be generated:
* `index.html`: split version of `README.bigb`, i.e. does not contain `h2`
* `toplevel to h2`: `h2.html`. Links to the split version of `h2`, since `h2` is also affected by the `splitDefault` of its parent, and therefore links to it use the split version by default
* `toplevel to notreadme`: `notreadme.html`. Links to non-split version of `notreadme.html` since that header is not `splitDefault`, because `splitDefault` does not propagate across includes
* `nosplit.html` non-split version of `README.bigb`, i.e. contains `h2`
* `toplevel to h2`: `#h2`, because even though `h2` is `splitDefault`, that header is already present in the current page, so it would be pointless to reload the split one
* `toplevel to notreadme`: `notreadme.html`
* `h2.html` split version of `h2` from `README.bigb`
* `notreadme.html`: non-split version of `notreadme.bigb`
* `notreadme to h2`: `h2.html`, because `h2` is `splitDefault`
* `notreadme to notreadme h2`: `#notreadme-h2`
* `notreadme-split.html`: split version of `notreadme.bigb`
* `notreadme to h2`: `h2.html`, because `h2` is `splitDefault`
* `notreadme to notreadme h2`: `notreadme.html#notreadme-h2`, because `notreadme-h2` is not `splitDefault`

The major application of this is that Ciro likes to work with a huge `README.bigb` containing thousands of random small topics. This is the case for example for: https://cirosantilli.com

And splitting those into separate source files would be quite laborious, as it would require duplicating IDs on the filename, and setting up \x[include]{p}.

However, after this README reaches a certain size, page loads start becoming annoyingly slow, even despite already loading large assets like \x[image]{p} video \x[video]{p} only on hover or click: the annoying slowness comes from the loading of the HTML itself before the browser can jump to the ID.

And even worse: this README corresponds to the main index page of the website, which will make what a large number of users will see be that slowness.

Therefore, once this README reaches a certain size, you can add the `splitDefault` attribute to it, to make things smoother for readers.

And if you have a smaller, more self-contained, and highly valuable tutorial such as https://cirosantilli.com/x86-paging[], you can just split that into a separate `.bigb` source file.

This way, any links into the smaller tutorial will show the entire page as generally desired.

And any links from the tutorial, back to the main massive README will link back to split versions, leading to fast loads.

This feature was implemented at: https://github.com/cirosantilli/ourbigbook/issues/131

= `\H` `splitSuffix` argument
{parent=h-arguments}

If given, add a custom suffix to the output filename of the header when using \x[split-headers].

If the given suffix is empty, it defaults to `-split`.

For example, given:
``
= my h1

== my h2
``
a `--split-headers` conversion would normally place `my h2` into a file called:
``
my-h2.html
``
However, if we instead wrote:
``
== my h2
{splitSuffix}
``
it would not be placed under:
``
my-h2-split.html
``
and if we set a custom one as:
``
== my h2
{splitSuffix=asdf}
``
it would go instead to:
``
my-h2-asdf.html
``

This option is useful if the root of your website is written in OurBigBook, and you want to both:
* have a section that talks about some other project
* host the documentation of that project inside the project source tree

For example, https://cirosantilli.com with source at https://github.com/cirosantilli/cirosantilli.github.io has a quick section about OurBigBook: https://cirosantilli.com#ourbigbook[].

Therefore, without a custom suffix, the split header version of that header would go to https://cirosantilli.com/ourbigbook[], which would collide with this documentation, that is present in a separate repository: https://github.com/cirosantilli/ourbigbook[].

Therefore a `splitSuffix` property is used, making the split header version fall under `/ourbigbook-split`, and leaving the nicer `/ourbigbook` for the more important project toplevel.

If given on the \x[the-toplevel-header]{p}, which normally gets a suffix by default to differentiate from the non-split version, it replaces the default `-split` suffix with a custom one.

For example if you had `notindex.bigb` as:
``
= Not index
``
then it would render to:
``
notindex-split.bigb
``
but if you used instead:
``
= Not index
{splitSuffix=asdf}
``
then it would instead be:
``
notindex-asdf.bigb
``

= `\H` `synonym` argument
{parent=h-arguments}

= Synonym
{synonym}

This option is similar to \x[h-title2-argument] but it additionally:
* creates a new ID that you can refer to, and renders it with the alternate chosen title
* the rendered ID on \x[internal-cross-reference]{p} is the same as what it is a synonym for
* the synonym header is not rendered at all, including in the \x[table-of-contents]
* when using \x[split-headers], a redirect output file is generated from the synonym to the main ID

Example:
``
= Parent

== GNU Debugger
{c}

= GDB
{c}
{synonym}

I like to say \x[gdb] because it is shorter than \x[gnu-debugger].
``
renders something like:
``
= GNU Debugger

I like to say \a[#gnu-debugger][GDB] because it is shorter than \x[#gnu-debugger][GNU Debugger].
``
Furthermore, if \x[split-headers] is used, another file is generated:
``
gdb.html
``
which contains a redirection from `gdb.html` to `gnu-debugger.html`.

Implemented at: https://github.com/cirosantilli/ourbigbook/issues/114

= `\H` `title` argument
{parent=h-synonym-argument}

Contains the main content of the header. The \x[insane-syntax]:
``
= My title
``
is equivalent to the sane:
``
\H[1][My title]
``
and in both cases `My title` is the title argument.

The title argument is also notably used for \x[automatic-id-from-title].

= Automatic ID from title
{parent=h-title-argument}

If a \x[the-toplevel-header][non-toplevel] macro has the `title` property is present but no explicit `id`, an ID is created automatically from the `title`, by applying the following transformations:
* do a \x[id-output-format] conversion on the title to remove for example any HTML tags that would be present in the conversion output
* convert all characters to lowercase. This uses \x[javascript-case-conversion]. Note that this does convert non-ASCII characters to lowercase, e.g. `É` to `é`.
* if \x[ourbigbook-json/id-normalize-latin] is `true` (the default) do \x[ourbigbook-json/latin-normalization]. This converts e.g. `é` to `e`.
* if \x[ourbigbook-json/id-normalize-punctuation] is `true` (the default) do \x[ourbigbook-json/punctuation-normalization]. This converts e.g. `+` to `plus`.
* convert consecutive sequences of all non `a-z0-9` ASCII characters to a single hyphen `-`. Note that this leaves non-ASCII characters untouched.
* strip leading or trailing hyphens
Note how those rules leave non-ASCII Unicode characters untouched, except for:
* capitalization changes wher applicable, e.g. `É` to `é`
as capitalization and determining if something "is a letter or not" in those cases can be tricky.

For toplevel headers, see: \x[the-id-of-the-first-header-is-derived-from-the-filename].

So for example, the following automatic IDs would be generated: \x[table-examples-of-automatically-generated-ids].

\Table{title=Examples of automatically generated IDs.}
[
|| title
|| id
|| latin normalization
|| punctuation normalization
|| comments

| My favorite title
| my-favorite-title
|
|
|

| Ciro's markdown is awesome
| ciro-s-markdown-is-awesome
|
|
| `'` is an ASCII character, but it is not in `a-z0-9`, therefore it gets converted to a hyphen `-`

| É你
| e你
| true
|
| The Latin https://en.wikipedia.org/wiki/Acute_accent[acute accented] `e`, `É`, is converted to its lower case form `é` as per the \x[javascript-case-conversion].

Then, due to \x[ourbigbook-json/latin-normalization], `é` is converted to `e`.

The Chinese character `你` is left untouched as Chinese characters have no case, and no ASCII analogue.

| É你
| é你
| false
|
| Same as the previous, but `é` is not converted to `e` since \x[ourbigbook-json/latin-normalization] is turned off.

| C++ is great
| c-plus-plus-is-great
|
| true
| This is the effect of \x[ourbigbook-json/punctuation-normalization].

| I \i[love] dogs.
| i-love-dogs
|
|
| `love` is extracted from the italic tags `love` with \x[id-output-format] conversion.
]

For \x[the-toplevel-header][the toplevel header], its ID is derived from the basename of the OurBigBook file without extension instead of from the `title` argument.

= `\H` `title2` argument of a synonym header
{parent=h-synonym-argument}

Unlike \x[h-title2-argument], the synonym does not show up by default next to the title. This is because we sometimes want that, and sometimes not. To make the title appear, you can simply add an empty `title2` argument to the synonym header as in:
``
= GNU Debugger
{c}

= GDB
{c}
{synonym}
{title2}

= Quantum computing

= Quantum computer
{synonym}
``
which renders something like:
``
= GNU Debugger (GDB)

= Quantum computing
``
Note how we added the synonym to the title only when it is not just a simple flexion variant, since `Quantum computing (Quantum computer)` would be kind of useless would be kind of useless.

= `\H` `tag` argument
{c}
{parent=h-arguments}
{tag=multiple-argument}

Same as \x[x-child-argument] but in the opposite direction, e.g.:
``
== Mammal

=== Bat
{tag=flying-animal}

=== Cat

== Flying animal
``
is equivalent in every way to:
``
== Mammal

=== Bat

=== Cat

== Flying animal
{child=bat}
``

Naming rationale:
* `parent` as the opposite of child is already taken to be then "main parent" via the "\x[h-parent-argument]"
* we could have renamed the \x[h-child-argument] to `tags` as in "this header tags that one", but it would be a bit confusing `tags` vs `tag`
So `child` vs `tag` it is for now.

You generally want to use `tag` instead of the \x[h-child-argument] because otherwise some very large header categories are going to contain Huge lists of children, which is not very nice when editing.

It is possible to enforce the \x[h-child-argument] or the \x[h-tag-argument] in a given project with the \x[ourbigbook-json/lint-h-tag] option.

= `\H` `title2` argument
{parent=h-arguments}

The `title2` argument can be given to any element that has the `title` argument.

Its usage is a bit like the `description=` argument of \x[image]{p}, allowing you to add some extra content to the header without affecting its ID.

Unlike `description=` however, `title2` shows up on all \x[x-full-argument][`full`] references, including appearances in the \x[table-of-contents], which make it more searchable.

Its primary use cases are:
* give acronyms, or other short names names of fuller titles such as mathematical/programming notation

One primary reason to not use the acronyms as the main section name is to avoid possible ID ambiguities with other acronyms.
* give the header in different languages

For example, given the OurBigBook input:
``
= Toplevel

The Toc follows:

== North Atlantic Treaty Organization
{c}
{title2=NATO}

\x[north-atlantic-treaty-organization]

\x[north-atlantic-treaty-organization]{full}
``
the rendered output looks like:
``
= Toplevel

The ToC follows:

* North Atlantic Treaty Organization (NATO)

== North Atlantic Treaty Organization (NATO)

North Atlantic Treaty Organization

Section 1. "North Atlantic Treaty Organization (NATO)"
``

Related alternatives to `title2` include:
* \x[h-disambiguate-argument] when you do want to affect the ID to remove ambiguities
* \x[h-synonym-argument]

Parenthesis are added automatically around all rendered `title2`.

The `title2` argument has a special meaning when applied to a \x[header] with the \x[h-synonym-argument], see \x[h-title2-argument-of-a-synonym-header].

\Comment[[[[
= `\H` `tutorial` argument
{parent=h-arguments}
{tag=boolean-argument}

This option is a convenience helper for the common use case of "writting a tutorial". The same would also apply to a report, or an article.
]]]]

= `\H` `wiki` argument
{parent=h-arguments}

If given, show a link to the Wikipedia article that corresponds to the header.

If a value is not given, automatically link to the Wiki page that matches the header exactly with spaces converted to underscores.

Here is an example with an explicit wiki argument:

``
==== Tiananmen Square
{wiki=Tiananmen_Square}
``

which looks like:

= Tiananmen Square
{id=wiki-explicit}
{parent=h-wiki-argument}
{wiki=Tiananmen_Square}

or equivalently with the value deduced from the title:

``
= Tiananmen Square
{wiki}
``

which looks like:

= Tiananmen Square
{id=wiki-implicit}
{parent=h-wiki-argument}
{wiki}

You can only link to subsections of wiki pages with explicit links as in:

``
= History of Tiananmen Square
{wiki=Tiananmen_Square#History}
``

which looks like:

= History of Tiananmen Square
{id=wiki-explicit-subsection}
{parent=h-wiki-argument}
{wiki=Tiananmen_Square#History}

= Header metadata section
{parent=header}

OurBigBook adds some header metadata to the toplevel header at the bottom of each page. this section describes this metadata.

Although the \x[table-of-contents]{child} has a macro to specify its placement, it is also automatically placed at the bottom of the page, and could be considered a header metadata section.

= Incoming links
{parent=header-metadata-section}

Lists other sections that link to the current section.

E.g. in:
``
= tmp

== tmp 1

=== tmp 1 1

=== tmp 1 2

\x[tmp-1]

== tmp 2

\x[tmp-1]
``
the page `tmp-1.html` would contain a list of incoming links as:
* `tmp-1-2`
* `tmp-2`
since those pages link to the `tmp-1` ID.

= Tagged
{parent=header-metadata-section}

Lists sections that are \x[secondary-children] of the current section, i.e. tagged under the current section.

The main header tree hierarchy descendants already show under the \x[table-of-contents] instead.

E.g. in:
``
= tmp

== Mammal

== Flying

== Animal

=== Bat
{tag=mammal}
{tag=flying}

=== Bee
{tag=flying}

=== Dog
{tag=mammal}
``
the tagged sections for:
* Mammal will contain Bat and Dog
* Flying will contain Bat and Bee

= Ancestors
{parent=header-metadata-section}

Shows a list of ancestors of the page. E.g. in:
``
= Asia

== China

=== Beijing

==== Tiananmen Square

=== Hong Kong
``
the ancestor lists would be for:
* Hong Kong: China, Asia
* Tiananmen Square: Beijing, China, Asia
* Beijing: China, Asia
* China: Asia
so we see that this basically provides a type of breadcrumb navigation.

= Image
{parent=macro}
{title2=`\Image` and `\image`}

A block image with \x[block-vs-inline-macros][capital] 'i' `Image` showcasing most of the image properties \x[image-my-test-image].
\OurbigbookExample[[
Have a look at this amazing image: \x[image-my-test-image].

\Image[Tank_man_standing_in_front_of_some_tanks.jpg]
{title=The title of my image.}
{id=image-my-test-image}
{width=600}
{height=200}
{source=https://en.wikipedia.org/wiki/File:Tianasquare.jpg}
{description=The description of my image.}
]]
This exemplifies the following parameters:
* `title`: analogous to the \x[h-title-argument]. Shows up preeminently, and sets a default ID if one is not given.
* \x[image-description-argument][`description`]: similar to `title`, but allow for further explanations without them appearing in \x[internal-cross-reference][cross references] to the image
* `source`: a standardized way to credit an image by linking to a URL that contains further image metadata
For further discussion on the effects of ID see: \x[image-id]{full}.

And this is how you make an inline image inline one with lower case `i`:
\OurbigbookExample[[
My inline \image[Tank_man_standing_in_front_of_some_tanks.jpg][test image] is awesome.
]]
Inline images can't have captions.

And now for an image outside of \x[ourbigbookexample] to test how it looks directly under \x[toplevel]: \x[image-my-test-image-toplevel]{full}.

\Image[Tank_man_standing_in_front_of_some_tanks.jpg]
{id=image-my-test-image-toplevel}

= Image height
{parent=image}

By default, we fix image heights to `height=315`, and let the `width` be calculated proportionally once the image loads. We therefore ignore the actual image size. This is done to:
* prevent reflows as the page loads images and can determine their actual sizes, especially is the user opens the page at a given ID in the middle of the page
* create a more uniform media experience by default, unless a custom image size is actually needed e.g. if the image needs to be larger

= Image ID
{parent=image}

Here is an image without a \x[image-description-argument][description] but with an ID so we can link to it: \x[image-my-test-image-2].
\OurbigbookExample[[
Have a look at this amazing image: \x[image-my-test-image-2].

\Image[Tank_man_standing_in_front_of_some_tanks.jpg]
{id=image-my-test-image-2}
]]
This works because \x[x-full-argument][`full` is the default cross reference style for `Image`], otherwise the link text would be empty since there is no `title`, and OurBigBook would raise an error.

OurBigBook can optionally deduce the title from the basename of the `src` argument if the `titleFromSrc` \x[boolean-argument] is given, or if `title-from-src` is set as the default \x[ourbigbook-json/media-providers][media provider] for the media type:
\OurbigbookExample[[
Have a look at this amazing image: \x[image-tank-man-standing-in-front-of-some-tanks].

\Image[Tank_man_standing_in_front_of_some_tanks.jpg]
{titleFromSrc}
]]

= Image caption
{parent=image-id}

If the image has neither \x[image-id][ID] nor title nor \x[image-description-argument][description] nor `source`, then it does not get a caption at all:
\OurbigbookExample[[
\Image[Tank_man_standing_in_front_of_some_tanks.jpg]
]]

If the image does not have an ID nor title, then it gets an automatically generated ID, just like every other OurBigBook output HTML element, and it is possible for readers to link to that ID on the rendered version, e.g. as:
``
#_123
``
Note that the `123` is not linked to the `Figure .`, but just a sequential ID that runs over all elements.

This type of ID is of course not stable across document revisions however, since if an image is added before that one, the link will break. So give an ID or title for anything that you expect users to link to.

Also, it is not possible to link to such images with an \x[internal-cross-reference], like any other OurBigBook element with autogenerated temporary IDs.

Another issue to consider is that in paged output formats like PDF, the image could float away from the text that refers to the image, so you basically always want to refer to image by ID, and not just by saying "the following image".

We can also see that such an image does not increment the Figure count:
\OurbigbookExample[[
\Image[Tank_man_standing_in_front_of_some_tanks.jpg]{id=image-my-test-image-count-before}
\Image[Tank_man_standing_in_front_of_some_tanks.jpg]
\Image[Tank_man_standing_in_front_of_some_tanks.jpg]{id=image-my-test-image-count-after}
]]

If the image has any visible metadata such as `source` or `description` however, then the caption does show and the Figure count gets incremented:
\OurbigbookExample[[
\Image[Tank_man_standing_in_front_of_some_tanks.jpg]{source=https://en.wikipedia.org/wiki/File:Tianasquare.jpg}
\Image[Tank_man_standing_in_front_of_some_tanks.jpg]{description=This is the description of my image.}
]]

= Where to store images
{parent=image}

= Store images inside the repository itself
{parent=where-to-store-images}

If you are making a limited repository that will not have a ton of images, then you can get away with simply git tracking your images in the main repository.

With this setup, no further action is needed. For example, with a file structure of:
``
./README.bigb
./Tank_man_standing_in_front_of_some_tanks.jpg
``
just use the image from \C[README.bigb] as:
\OurbigbookExample[[
\Image[Tank_man_standing_in_front_of_some_tanks.jpg]
]]

However, if you are making a huge tutorial, which can have a huge undefined number of images (i.e. any scientific book), then you likely don't want to git track your images in the git repository.

A generally better alternative is to \x[store-images-in-a-separate-media-repository], and especially \x[store-images-in-a-separate-media-repository-and-track-it-as-a-git-submodule].

= Store images in a separate media repository
{parent=where-to-store-images}

In this approach, you create a separate GitHub repository in addition to the main one containing the text to contain only media such as images.

This approach is more suitable than \x[store-images-inside-the-repository-itself] if you are going to have a lot of images.

When using this approach, you could of course just point directly to the final image URL, e.g. as in:
\OurbigbookExample[[
\Image[https://raw.githubusercontent.com/cirosantilli/media/master/Chrysanthemum_Xi_Jinping_with_black_red_liusi_added_by_Ciro_Santilli.jpg]
]]
but OurBigBook allows you use configurations that allow you to enter just the image basename: `Chrysanthemum_Xi_Jinping_with_black_red_liusi_added_by_Ciro_Santilli.jpg` which we will cover next.

In order to get this to work, the recommended repository setup is:
* `./main-repo/.git`: main repository at https://github.com/username/main-repo
* `./main-repo/data/media/.git/`: media repository at https://github.com/username/main-repo-media[], and where `data/` is gitignored.
The directory and repository names are not mandatory, but if you place media in `data/media` and name its repository by adding the `*-media` suffix, then `ourbigbook` will handle everything for you without any further configuration in \x[ourbigbook-json/media-providers].

This particular documentation repository does have a different setup as can be seen from its \a[ourbigbook.json]. Then, when everything is setup correctly, we can refer to images simply as:
\OurbigbookExample[[
\Image[Chrysanthemum_Xi_Jinping_with_black_red_liusi_added_by_Ciro_Santilli.jpg]{provider=github}
]]
In this example, we also needed to set `{provider=github}` explicitly since it was not set as the default image provider in our `ourbigbook.json`. In most projects however, all of your images will be in the default repository, so this won't be needed.

`provider` must not be given when a full URL is given because we automatically detect providers from URLs, e.g.:
``
\Image[https://raw.githubusercontent.com/cirosantilli/media/master/Chrysanthemum_Xi_Jinping_with_black_red_liusi_added_by_Ciro_Santilli.jpg]{provider=github}
``
is an error.

TODO implement: `ourbigbook` will even automatically add and push used images in the `my-tutorial-media` repository for you \x[publish][during publishing]!

You should then use the following rules inside `my-tutorial-media`:
* give every file a very descriptive and unique name as a full English sentence
* never ever delete any files, nor change their content, unless it is an improvement in format that does change the information contained of the image TODO link to nice Wikimedia Commons guideline page
This way, even though the repositories are not fully in sync, anyone who clones the latest version of the `*-media` directory will be able to view any version of the main repository.

Then, if one day the media repository ever blows up GitHub's limit, you can just migrate the images to another image server that allows arbitrary basenames, e.g. AWS, and just configure your project to use that new media base URL with the \x[ourbigbook-json/media-providers] option.

The reason why images should be kept in a separate repository is that images are hundreds or thousands of times larger than hand written text.

Therefore, images could easily fill up the maximum repository size you are allowed: https://webapps.stackexchange.com/questions/45254/file-size-and-storage-limits-on-github#84746 and then what will you do when GitHub comes asking you to reduce the repository size?

https://git-lfs.github.com/[Git LFS] is one approach to deal with this, but we feel that it adds too much development overhead.

= Store images in a separate media repository and track it as a git submodule
{parent=store-images-in-a-separate-media-repository}

This is likely the sanest approach possible, as it clearly specifies which media version matches which repository version through the submodule link.

Furthermore, it is possible to make the submodule clone completely optional by setting things up as follows. For your OurBigBook project `yourname/myproject` create a `yourname/myproject-media` with the media, and track it as a submodule under `yourname/myproject/media`.

Then, add to \x[ourbigbook-json/media-providers]:
```
"media-providers": {
"github": {
"default-for": ["image", "video"],
"path": "media",
"remote": "yourname/myproject-media"
}
}
```

Now, as mentioned at \x[ourbigbook-json/media-providers], everything will work beautifully:

* `ourbigbook .` local conversion will use images from `media/` if it exists, e.g.:
```
\Image[myimage.jpg]
```
will render `media/myimage.jpg`. So after cloning the submodule, you will be able to see the images on the rendered pages without an internet connection.

But if the submodule is not cloned, not problem, renders will detect that and automatically use GitHub images.

Then, when you do:
```
ourbigbook --publish
```
the following happen:
* `\Image[myimage.jpg]` uses the GitHub URL
* automatically push `media/` to GitHub in case there were any updates
* also, that directory is automatically gitignore, so it won't be pushed as part of the main render and thus duplicate things

= Store images in Wikimedia Commons
{parent=where-to-store-images}

Wikimedia Commons is another great possibility to upload your images to:
\OurbigbookExample[[
\Image[https://upload.wikimedia.org/wikipedia/commons/thumb/5/5b/Gel_electrophoresis_insert_comb.jpg/450px-Gel_electrophoresis_insert_comb.jpg]
{source=https://commons.wikimedia.org/wiki/File:Gel_electrophoresis_insert_comb.jpg}
]]

OurBigBook likes Wikimedia Commons so much that we automatically parse the image URL and if it is from Wikimedia Commons, automatically deduce the `source` for you. So the above image renders the same without the `source` argument:
\OurbigbookExample[[
\Image[https://upload.wikimedia.org/wikipedia/commons/5/5b/Gel_electrophoresis_insert_comb.jpg]
]]

And like for non-Wikimedia images, you can automatically generate a `title` from the `src` by setting the `titleFromSrc` \x[boolean-argument] or if `title-from-src` is set as the default \x[ourbigbook-json/media-providers][media provider] for the media type:
\OurbigbookExample[[
\Image[https://upload.wikimedia.org/wikipedia/commons/5/5b/Gel_electrophoresis_insert_comb.jpg]
{titleFromSrc}
]]

And a quick test for a more complex thumb resized URL:
\OurbigbookExample[[
\Image[https://upload.wikimedia.org/wikipedia/commons/thumb/5/5b/Gel_electrophoresis_insert_comb.jpg/450px-Gel_electrophoresis_insert_comb.jpg]
]]

If you really absolutely want to turn off the `source`, you can explicitly set:
\OurbigbookExample[[
\Image[https://upload.wikimedia.org/wikipedia/commons/5/5b/Gel_electrophoresis_insert_comb.jpg]
{source=}
]]
but you don't want to do that for the most commonly Wikimedia Commons used license of CC BY+, do you? :-)

Upsides of using Wikimedia Commons for your images:
* makes it easier for other writers to find and reuse your images
* automatically generates resized versions of the uploaded images into several common dimensions so you can pick the smallest one that fits your desired \x[image-height] to reduce bandwidth usage
* if you have so many images that they would blow even the size of a \x[store-images-in-a-separate-media-repository][separate media repository], this will still work
Downsides:
* forces you to use the Creative Commons license
* requires the content to be educational in nature
* uploading a bunch of images to Wikimedia Commons does feel a bit more laborious than it should because you have to write down so much repeated metadata for them

= Image lazy loading
{parent=image}

We do this by default because OurBigBook is meant to allow producing huge single page documents like Ciro likes it, and in this way:
* images that the user is looking at will load first
* we save a lot of bandwidth for the user who only wants to browse one section

TODO: maybe create a mechanism to disable this for the entire build with \x[ourbigbook-json].

= Background color of transparent images
{parent=image}

For the love of God, there is no standardized for SVG to set its background color without a rectangle? https://stackoverflow.com/questions/11293026/default-background-color-of-svg-root-element `viewport-fill` was just left in limbo?

And as a result, many many many SVG online images that you might want to reuse just rely on white pages and don't add that background rectangle.

Therefore for now we just force white background on \x[overview-of-files-in-this-repository][our default CSS], which is what most SVGs will work with. Otherwise, you can lose the entire image to our default black background.

Then if someone ever has an SVG that needs another background color, we can add an image attribute to set that color as a local style.

= Image generators
{parent=image}

TODO implement: mechanism where you enter a textual description of the image inside the code body, and it then converts to an image, adds to the `-media` repo and pushes all automatically. Start with dot.

https://github.com/cirosantilli/ourbigbook/issues/40

= Image argument
{parent=image}

= Image `check` argument
{parent=image-argument}
{tag=named-argument}
{tag=boolean-argument}

Analogous to the \x[a-check-argument] when checking if the \x[image-src-argument] exists or not.

= Image `description` argument
{parent=image-argument}
{tag=named-argument}

The `description` argument similar to the \x[image-title-argument] argument, but allows allowing longer explanations without them appearing in \x[internal-cross-reference][cross references] to the image.

For example, consider:
\OurbigbookExample[[
See this image: \x[image-description-argument-test-1].

\Image[Tank_man_standing_in_front_of_some_tanks.jpg]
{title=Tank man standing in front of some tanks.}
{id=image-description-argument-test-1}
{description=Note how the tanks are green.}
{source=https://en.wikipedia.org/wiki/File:Tianasquare.jpg}
]]
In this example, the reference `\x[image-description-argument-test-1]` expands just to
\Q[Tank man standing in front of some tanks]
and does not include the description, which only shows on the image.

The description can be as large as you like. If it gets really large however, you might want to consider moving the image to its own header to keep things slightly saner. This will be especially true after we eventually do: https://github.com/cirosantilli/ourbigbook/issues/180[].

If the description contains any element that would take its own separate line, like multiple paragraphs or a list, we automatically add a line grouping the description with the corresponding image to make that clearer, otherwise it can be hard to know which title corresponds to a far away image. Example with multiple paragraphs:
\OurbigbookExample[[
Stuff before the image.

\Image[Tank_man_standing_in_front_of_some_tanks.jpg]
{title=Tank man standing in front of some tanks.}
{id=image-description-argument-test-2}
{source=https://en.wikipedia.org/wiki/File:Tianasquare.jpg}
{description=Note how the tanks are green.

But the shirt is white.}

Stuff after the image description.
]]

= Image `src` argument
{parent=image-argument}
{tag=positional-argument}

The address of the image, e.g. in:
``
\Image[image.png]
``
the `src` is `image.png`.

Analogous to the \x[a-href-argument].

= Image `title` argument
{parent=image-argument}

Analogous to the \x[h-title-argument].

= Include
{title2=`\Include`}
{parent=macro}

The `\Include` macro allows including an external OurBigBook headers under the current header.

It exists to allow optional single page HTML output while still retaining the ability to:
* split up large input files into multiple files to make renders faster during document development
* suggest an optional custom output split with one HTML output per OurBigBook input, in order to avoid extremely large HTML pages which could be slow to load

`\Include` takes one mandatory argument: the ID of the section to be included, much like \x[internal-cross-reference]{p}.

There is however one restriction: only \x[the-toplevel-header]{p} can be pointed to. This restriction allows us to easily find the included file in the filesystem, and dispenses the need to do a first `./ourbigbook` run to generate the \x[internal-cross-file-reference-internals][ID database]. This works because \x[the-id-of-the-first-header-is-derived-from-the-filename].

Headers of the included document are automatically shifted to match the level of the child of the level where they are being included.

If \x[embed-includes] is given, the external document is rendered embedded into the current document directly, essentially as if the source had been copy pasted (except for small corrections such as the header offsets).

Otherwise, the following effects happen:
* The headers of the included tree appear in the \x[table-of-contents] of the document as links to the corresponding external files.

This is implemented simply by reading a previously generated database file much like \x[internal-cross-file-reference-internals], which avoids the slowdown of parsing all included files every time.

As a result, you have to do an initial parse of all files in the project to extract their headers however, just as you would need to do when linking to those headers.
* the include itself renders as a link to the included document
* \x[embed-includes]

Here is an example of inclusion of the files `not-readme.bigb` and `not-readme-2.bigb`:
``
\Include[not-readme]
\Include[not-readme-2]
\Include[not-readme-with-scope]
``
The above is the recommended and slightly \x[insane-macro-shortcuts][insaner] version of:
``
\Include[not-readme]

\Include[not-readme-2]

\Include[not-readme-with-scope]
``
The insaner version is a bit insaner because the `\Include` magically discards the following newline node that follows it if it just a plaintext node containing exactly a newline. With a double newline, the newline would already have been previously taken out on the lexing stage as part of a paragraph.

\x[include-example]{full} shows what those actually render like.

= `\Include` from subdirectories
{parent=include}

When you are in a subdirectory, include resolution just is simply relative to the subdirectory. E.g. we could do:

subdir/index.bigb
``
= Subdir

\Include[notindex]
\Include[subdir2/notindex]
``

subdir/notindex.bigb
``
= Notindex
``

subdir/subdir2/notindex.bigb
``
= Notindex
``

It is not currently possible to include from ancestor directories: https://github.com/cirosantilli/ourbigbook/issues/214[].

= `\Include` `parent` argument
{parent=include}

This option is analogous to \x[h-parent-argument], but for \x[include]{p}.

For example, consider you have:
``
= Animal

== Dog

== Cat

== Bat
``
and now you want to split `Cat` to `cat.bigb`.

If you wrote:
``
= Animal

== Dog

\Include[cat]

== Bat
``
Cat would be a child of Dog, since that is the previous header, which is not what we want.

Instead, we want to write:
``
= Animal

== Dog

\Include[cat]{parent=animal}

== Bat
``
and now Cat will be a child of Animal as desired.

Implemented at: https://github.com/cirosantilli/ourbigbook/issues/127

= `\Include` example
{parent=include}

This shows what includes render as.

\Include[not-readme]
\Include[not-readme-2]
\Include[not-readme-with-scope]
\Include[subdir]
\Include[subdir/notindex]

= Italic
{parent=macro}
{title2=`\i`}

\OurbigbookExample[[
Some \i[italic] text.
]]

= `\JsCanvasDemo`
{parent=macro}

The `JsCanvasDemo` macro allows you to create interactive HTML/JavaScript https://en.wikipedia.org/wiki/Canvas_element[canvas] demos easily.

These demos:
* only start running when the user scrolls over them for the first time
* stop automatically when they leave the viewport
so you can stuff as many of them as you want on a page, and they won't cause the reader's CPU to fry an egg.

\OurbigbookExample[[[
\JsCanvasDemo[[
new class extends OurbigbookCanvasDemo {
init() {
super.init('hello');
this.pixel_size_input = this.addInputAfterEnable(
'Pixel size',
{
'min': 1,
'type': 'number',
'value': 1,
}
);
}
draw() {
var pixel_size = parseInt(this.pixel_size_input.value);
for (var x = 0; x < this.width; x += pixel_size) {
for (var y = 0; y < this.height; y += pixel_size) {
var b = ((1.0 + Math.sin(this.time * Math.PI / 16)) / 2.0);
this.ctx.fillStyle =
'rgba(' +
(x / this.width) * 255 + ',' +
(y / this.height) * 255 + ',' +
b * 255 +
',255)'
;
this.ctx.fillRect(x, y, pixel_size, pixel_size);
}
}
}
}
]]
]]]

And another one showing off some https://developer.mozilla.org/en-US/docs/Web/API/WebGL_API[WebGL]:

\JsCanvasDemo[[
new class extends OurbigbookCanvasDemo {
init() {
super.init('webgl', {context_type: 'webgl'});
this.ctx.viewport(0, 0, this.ctx.drawingBufferWidth, this.ctx.drawingBufferHeight);
this.ctx.clearColor(0.0, 0.0, 0.0, 1.0);
this.vertexShaderSource = `
#version 100
precision highp float;
attribute float position;
void main() {
gl_Position = vec4(position, 0.0, 0.0, 1.0);
gl_PointSize = 64.0;
}
`;

this.fragmentShaderSource = `
#version 100
precision mediump float;
void main() {
gl_FragColor = vec4(0.18, 0.0, 0.34, 1.0);
}
`;
this.vertexShader = this.ctx.createShader(this.ctx.VERTEX_SHADER);
this.ctx.shaderSource(this.vertexShader, this.vertexShaderSource);
this.ctx.compileShader(this.vertexShader);
this.fragmentShader = this.ctx.createShader(this.ctx.FRAGMENT_SHADER);
this.ctx.shaderSource(this.fragmentShader, this.fragmentShaderSource);
this.ctx.compileShader(this.fragmentShader);
this.program = this.ctx.createProgram();
this.ctx.attachShader(this.program, this.vertexShader);
this.ctx.attachShader(this.program, this.fragmentShader);
this.ctx.linkProgram(this.program);
this.ctx.detachShader(this.program, this.vertexShader);
this.ctx.detachShader(this.program, this.fragmentShader);
this.ctx.deleteShader(this.vertexShader);
this.ctx.deleteShader(this.fragmentShader);
if (!this.ctx.getProgramParameter(this.program, this.ctx.LINK_STATUS)) {
console.log('error ' + this.ctx.getProgramInfoLog(this.program));
return;
}
this.ctx.enableVertexAttribArray(0);
var buffer = this.ctx.createBuffer();
this.ctx.bindBuffer(this.ctx.ARRAY_BUFFER, buffer);
this.ctx.vertexAttribPointer(0, 1, this.ctx.FLOAT, false, 0, 0);
this.ctx.useProgram(this.program);
}
draw() {
this.ctx.clear(this.ctx.COLOR_BUFFER_BIT);
this.ctx.bufferData(this.ctx.ARRAY_BUFFER, new Float32Array([Math.sin(this.time / 60.0)]), this.ctx.STATIC_DRAW);
this.ctx.drawArrays(this.ctx.POINTS, 0, 1);
}
}
]]

= List
{parent=macro}
{title2=`* `, `\L`, `\Ul`, `\Ol`}

\x[insane-macro-shortcuts][Insane] with `* ` (asterisk space):
\OurbigbookExample[[
* a
* b
* c
]]

Equivalent saner with \x[auto-parent][implicit `ul` container]:
\OurbigbookExample[[
\L[a]
\L[b]
\L[c]
]]

Equivalent fully sane with explicit container:
\OurbigbookExample[[
\Ul[
\L[a]
\L[b]
\L[c]
]
]]

The explicit container is required if you want to pass extra arguments properties to the `ul` list macro, e.g. a title and an ID: \x[list-my-id]{full}:
\OurbigbookExample[[
\Ul
{id=list-my-id}
[
\L[a]
\L[b]
\L[c]
]
]]
This is the case because without the explicit container in an implicit `ul` list, the arguments would stick to the last list item instead of the list itself.

It is also required if you want ordered lists:
\OurbigbookExample[[
\Ol[
\L[first]
\L[second]
\L[third]
]
]]

Insane nested list with two space indentation:
\OurbigbookExample[[
* a
* a1
* a2
* a2
* b
* c
]]
The indentation must always be exactly equal to two spaces, anything else leads to errors or unintended output.

Equivalent saner nested lists with implicit containers:
\OurbigbookExample[[
\L[
a
\L[a1]
\L[a2]
\L[a2]
]
\L[b]
\L[c]
]]

Insane list item with a paragraph inside of it:
\OurbigbookExample[[
* a
* I have

Multiple paragraphs.

* And
* also
* a
* list
* c
]]

Equivalent sane version:
\OurbigbookExample[[
\L[a]
\L[
I have

Multiple paragraphs.

\L[And]
\L[also]
\L[a]
\L[list]
]
\L[c]
]]

Insane lists may be escaped with a backslash as usual:
\OurbigbookExample[[
\* paragraph starting with an asterisk.
]]

You can also start insane lists immediately at the start of a \x[positional-vs-named-arguments][positional or named argument], e.g.:
\OurbigbookExample[[
\P[* a
* b
* c
]
]]

And now a list outside of \x[ourbigbookexample] to test how it looks directly under \x[toplevel]:

\L[a]
\L[b]
\L[c]

= Mathematics
{parent=macro}
{title2=`$$`, `$`, `\M`, `\m`}

Via https://katex.org/[KaTeX] server side, oh yes!

Inline math is done with the dollar sign (`$`) \x[insane-macro-shortcuts][insane macro shortcut]:
\OurbigbookExample[[
My inline $\sqrt{1 + 1}$ is awesome.
]]
and block math is done with two or more dollar signs (`$$`):
\OurbigbookExample[[
$$
\sqrt{1 + 1} \\
\sqrt{1 + 1}
$$
]]

The sane version of inline math is a lower case `m`:
\OurbigbookExample[[[
My inline \m[[\sqrt{1 + 1}]] is awesome.
]]]
and the sane version of block math is with an upper case `M`:
\OurbigbookExample[[[
\M[[
\sqrt{1 + 1} \\
\sqrt{1 + 1}
]]
]]]

The capital vs lower case theme is also used in other elements, see: \x[block-vs-inline-macros].

In the sane syntax, \x[escape-characters][as with any other argument], you have to either escape any closing square brackets `]` with a backslash `\`:
\OurbigbookExample[[
My inline \m[1 - \[1 + 1\] = -1] is awesome.
]]
or with the equivalent double open and close:
``
My inline \m[[1 - [1 + 1] = -1]] is awesome.
``

HTML escaping happens as you would expect, e.g. < shows fine in:
\OurbigbookExample[[
$$
1 < 2
$$
]]

Equation IDs and titles and linking to equations works identically to \x[image]{p}, see that section for full details. Here is one equation reference example that links to the following insane syntax equation: \x[equation-my-first-insane-equation]:
\OurbigbookExample[[
$$
\sqrt{1 + 1}
$$
{title=My first insane equation.}
]]
and the sane equivalent \x[equation-my-first-sane-equation]:
\OurbigbookExample[[[
\M{title=My first sane equation.}[[
\sqrt{1 + 1}
]]
]]]

Here is a raw one just to test the formatting outside of a `ourbigbook_comment`:
$$\sqrt{1 + 1}$$

= Math defines across blocks
{parent=mathematics}

First here is an invisible block (with `{show=0}`) defining with a `\newcommand` definition after this paragraph:
\OurbigbookExample[[
$$
\newcommand{\foo}[0]{bar}
$${show=0}
]]
We make it invisible because this block only contains KaTeX definitions, and should not render to anything.

Then the second math block uses those definitions:
\OurbigbookExample[[
$$
\foo
$$
]]

Analogously with `\def`, definition:
\OurbigbookExample[[
$$
\gdef\foogdef{bar}
$${show=0}
]]
and the second block using it:
\OurbigbookExample[[
$$
\foogdef
$$
]]

And just to test that `{show=1}` actually shows, although it is useless, and that `{show=0}` skips incrementing the equation count:
\OurbigbookExample[[
$$1 + 1$${show=1}
$$2 + 2$${show=0}
$$3 + 3$${show=1}
]]

= `ourbigbook.tex`
{parent=mathematics}

If your project has multiple `.bigb` input files, you can share Mathematics definitions across all files by adding them to the `ourbigbook.tex` file on the toplevel directory.

For example, if `ourbigbook.tex` contains:
``
\newcommand{\foo}[0]{bar}
``
then from any `.bigb` file we in the project can use:
``
$$
\foo
$$
``

= Paragraph
{title2=`\P`}
{parent=macro}

OK, this is too common, so we opted for some \x[insane-macro-shortcuts][insanity] here: double newline is a paragraph!
\OurbigbookExample[[
Paragraph 1.

Paragraph 2.
]]

Equivalently however, you can use an explicit `\P` macros as well, which is required for example to add properties to a paragraph, e.g.:
\OurbigbookExample[[
\P{id=paragraph-1}[Paragraph 1]
\P{id=paragraph-2}[Paragraph 2]
]]

Paragraphs are created automatically inside \x[macro-argument-syntax][macro argument] whenever a double newline appears.

Note that OurBigBook paragraphs render in HTML as `div` with `class="p"` and not as `p`. This means that you can add basically anything inside them, e.g. a list:
``
My favorite list is:
\Ul[
\li[aa]
\li[bb]
]
because it is simple.
``
which renders as a single paragraph.

One major advantage of this, is that when writing documentation, you often want to keep lists or code blocks inside a given paragraph, so that it is easy to reference the entire paragraph with an ID. Think for example of paragraphs in the C++ standard.

= Passthrough
{parent=macro}
{title2=`\passthrough`}

Dumps its contents directly into the rendered output.

This construct is not XSS safe, see: \x[unsafe-xss]{full}.

Here for example we define a paragraph in raw HTML:
\OurbigbookExample[[[
\passthrough[[

Hello raw HTML!


]]
]]]

And for an inline passthrough:
\OurbigbookExample[[[
Hello \passthrough[[raw]] world!
]]]

= Quotation
{parent=macro}
{title2=`\Q`}

With `q`:
\OurbigbookExample[[
And so he said:

\Q[
Something very smart

And with multiple paragraphs.
]

and it was great.
]]

= Table
{parent=macro}
{title2=`|| `, `| `, `\Table`, `\Tr`, `\Th` and `\Td`}

The \x[insane-code-and-math-shortcuts][insane] syntax marks:
* headers with `|| ` (pipe, pipe space) at the start of a line
* regular cells with `| ` (pipe, space) at the start of a line
* separates rows with double newline
For example:
\OurbigbookExample[[
|| Header 1
|| Header 2

| 1 1
| 1 2

| 2 1
| 2 2
]]
Empty cells are allowed without the trailing space however:
\OurbigbookExample[[
| 1 1
|
| 1 3

| 2 1
|
| 2 3
]]

Equivalent fully explicit version:
\OurbigbookExample[[
\Table[
\Tr[
\Th[Header 1]
\Th[Header 2]
]
\Tr[
\Td[1 1]
\Td[1 2]
]
\Tr[
\Td[2 1]
\Td[2 2]
]
]
]]
Any white space indentation inside an explicit `\Tr` can make the code more readable, and is automatically removed from final output due to \x[remove-whitespace-children] which is set for `\Table`.

To pass further arguments to an implicit table such as `title` or `id`, you need to use an explicit `table` macro as in: \x[table-my-table].
\OurbigbookExample[[
\Table
{title=My table title.}
{id=table-my-table}
[
|| Header 1
|| Header 2

| 1 1
| 1 2

| 2 1
| 2 2
]
]]
We would like to remove that explicit toplevel requirement as per: https://github.com/cirosantilli/ourbigbook/issues/186[] The rules of when the caption shows up or not similar to those of \x[image]{p} as mentioned at \x[image-caption]{full}.

Multiple source lines, including paragraphs, can be added to a single cell with insane syntax by indenting the cell with exactly two spaces just as for \x[list]{p}, e.g.:
\OurbigbookExample[[
|| h1
|| h2
|| h3

h3 2

| 11
| 12

12 2
| 13

| 21
| 22
| 23
]]
Arbitrarily complex nested constructs may be used, e.g. a table inside a list inside table:
\OurbigbookExample[[
| 00
| 01

* l1
* l2

| 20
| 21

| 30
| 31

| 10
| 11
]]

And now a table outside of \x[ourbigbookexample] to test how it looks directly under \x[toplevel]:

\Table{title=My table title.}
[
\Tr[
\Th[Header 1]
\Th[Header 2]
]
\Tr[
\Td[1 1]
\Td[1 2]
]
\Tr[
\Td[2 1]
\Td[2 2]
]
]

And a fully insane one:

|| Header 1
|| Header 2

| 1 1
| 1 2

| 2 1
| 2 2

= Table sorting
{parent=table}

JavaScript interactive on-click table sorting is enabled by default, try it out by clicking on the header row:
\OurbigbookExample[[
|| String col
|| Integer col
|| Float col

| ab
| 2
| 10.1

| a
| 10
| 10.2

| c
| 2
| 3.4
]]
Powered by: https://github.com/tristen/tablesort

= Table of contents
{parent=macro}
{title2=`\Toc`}

OurBigBook automatically adds a ToC at the end of the first \x[the-toplevel-header][non-toplevel header] of every document.

For example, on a standard document with a single toplevel header:
``
= Animal

Animals are cute!

== Dog

== Cat
``
the ToC is rendered like:
``
= Animal

Animals are cute!

Table of Contents
* Dog
* Cat

== Dog

== Cat
``

You may customize ToC placement with `\Toc` macro, but just don't do it, it will just go against common convention and confuse readers.

This is especially important when considering \x[split-headers], where you almost always want an automatically generated ToC for every split header, otherwise you would need to add them all manually.

Only one ToC is rendered per document. Any ToC besides the first one is ignored. In particular, this means that \x[include]{p} with \x[embed-includes] work seamlessly and render a single table of contents, even if multiple `\Toc` macros are present in the included pages.

The \x[internal-cross-reference][ID] of the ToC is always fixed to `#toc`. If you try to use that for another element, you will get the following error:
``
error: tmp.bigb:3:1: reserved ID "toc"
``

The ToC ignores \x[the-toplevel-header] if you have one.

For when you want a quick outline of the header tree on the terminal, also consider the \x[log-headers] option.

= Table of contents JavaScript open close interaction
{parent=table-of-contents}

To the left of table of content entries you can click on an open/close icon to toggle the visibility of different levels of the table of contents.

The main use case covered by the expansion algorithm is as follows:
* the page starts with all nodes open to facilitate Ctrl + F queries
* if you click on a node in that sate, you close all its children, to get a summarized overview of the contents
* if you click one of those children, it opens only its own children, so you can interactively continue exploring the tree

The exact behaviour is:
* the clicked node is open:
* state 1 all children are closed. Action: open all children recursively, which puts us in state 2
* state 2: not all children are closed. Action close all children, which puts us in state 1. This gives a good overview of the children, without any children of children getting in the way.
* state 3: the clicked node is closed (not showing any children). Action: open it to show all direct children, but not further descendants (i.e. close those children). This puts us in state 1.

Note that those rules make it impossible to close a node by clicking on it, the only way to close a node os to click on its parent, the state transitions are:
* 3 -> 1
* 1 -> 2
* 2 -> 1
but we feel that it is worth it to do things like this to cover the main use case described above without having to add two buttons per entry.

Clicking on the link from a \x[header] up to the table of contents also automatically opens up the node for you in case it had been previously closed manually.

= Video
{parent=macro}
{title2=`\Video` and `\video`}

Very analogous to \x[image]{p}, only differences will be documented here.

In the case of videos, \x[where-to-store-images] becomes even more critical since videos are even larger than images, such that the following storage approaches are impractical off the bat:
* \x[store-images-inside-the-repository-itself]
* \x[store-images-in-a-separate-media-repository]
As a result, then https://commons.wikimedia.org[Wikimedia Commons] is one of the best options \x[store-images-in-wikimedia-commons][much like for images]:
\OurbigbookExample[[
\Video[https://upload.wikimedia.org/wikipedia/commons/8/85/Vacuum_pump_filter_cut_and_place_in_eppendorf.webm]
{id=sample-video-in-wikimedia-commons}
{title=Nice sample video stored in Wikimedia Commons.}
{start=5}
]]
We also handle more complex transcoded video URLs just fine:
\OurbigbookExample[[
\Video[https://upload.wikimedia.org/wikipedia/commons/transcoded/1/19/Scientific_Industries_Inc_Vortex-Genie_2_running.ogv/Scientific_Industries_Inc_Vortex-Genie_2_running.ogv.480p.vp9.webm]
{id=sample-video-in-wikimedia-commons-transcoded}
{title=Nice sample video stored in Wikimedia Commons transcoded.}
]]
Commons is better than YouTube if your content is on-topic there because:
* they have no ads
* it allows download of the videos: https://www.quora.com/Can-I-download-Creative-Commons-licensed-YouTube-videos-to-edit-them-and-use-them[].
* it makes it easier for other users to find and re-use your videos

If your video does not fit the above Wikimedia Commons requirements, YouTube could be a good bet. OurBigBook https://github.com/cirosantilli/ourbigbook/issues/50[automatically detects YouTube URLs] for you, so the following should just work:
\OurbigbookExample[[
\Video[https://youtube.com/watch?v=YeFzeNAHEhU&t=38]
{id=sample-video-from-youtube-implicit-youtube}
{title=Nice sample video embedded from YouTube implicit from `youtube.com` URL.}
]]
The `youtu.be` domain hack URLs also work;
\OurbigbookExample[[
\Video[https://youtu.be/YeFzeNAHEhU?t=38]
{id=sample-video-from-youtube-implicit-youtu-be}
{title=Nice sample video embedded from YouTube implicit from `youtu.be` URL.}
]]
Alternatively, you can reach the same result in a more explicit and minimal way by setting `{provider=youtube}` and the \x[video-start-argument][`start`] arguments:
\OurbigbookExample[[
\Video[YeFzeNAHEhU]{provider=youtube}
{id=sample-video-from-youtube-explicit}
{title=Nice sample video embedded from YouTube with explicit `youtube` argument.}
{start=38}
]]
When the `youtube` provider is selected, the Video address should only to contain the YouTube video ID, which shows in the YouTube URL for the video as:
``
https://www.youtube.com/watch?v=
``
Remember that you can also enable the `youtube` provider by default on your \x[ourbigbook-json] with:
``
"media-provider" {
"youtube": {"default-for": "video"}
}
``

But you can also use raw video files from any location that can serve them of course, e.g. here is one stored in this repository: \x[sample-video-in-repository].
\OurbigbookExample[[
\Video[Tank_man_side_hopping_in_front_of_some_tanks.mp4]
{id=sample-video-in-repository}
{title=Nice sample video stored in this repository.}
{source=https://www.youtube.com/watch?v=YeFzeNAHEhU}
{start=3}
]]

And as for images, setting `titleFromSrc` automatically calculates a title for you:
\OurbigbookExample[[
\Video[Tank_man_side_hopping_in_front_of_some_tanks.mp4]
{titleFromSrc}
{source=https://www.youtube.com/watch?v=YeFzeNAHEhU}
]]

= Video lazy loading
{parent=video}

Unlike \x[image-lazy-loading], we don't support video lazy loading yet because:
* non-`youtube` videos use the `video` tag which has no `loading` property yet
* `youtube` videos are embedded with `iframe` and `iframe` has no `loading` property yet

Both of this cases could be worked around with JavaScript:
* non-`youtube`: set `src` from JavaScript as shown for images: https://stackoverflow.com/questions/2321907/how-do-you-make-images-load-lazily-only-when-they-are-in-the-viewport/57389607#57389607[].

But this breaks page semantics however, we don't know how to work around that
* `youtube` videos: same as above for the `iframe`, but this should be less problematic since YouTube videos are not viewable without JavaScript anyways, and who cares about `iframe` semantics?

= `\Video` `start` argument
{parent=video}

The time to start playing the video at in seconds. Works for both `youtube` and non-YouTube videos.

= Internal cross reference
{parent=macro}

= `\x` macro
{title2}
{synonym}

Every macro in OurBigBook can have an optional `id` and many also have a reserved `title` property.

When a macro in the document has a `title` argument but no `id` argument given, get an auto-generated ID from the title: \x[automatic-id-from-title].

For macros that do have an ID, derived from `title` or not, you can write a cross reference to it, e.g.:
\OurbigbookExample[[
See this \x[internal-cross-reference]{p} awesome section.
]]

An explicit link body can be given just as for regular HTTP \x[link]{p} as:
\OurbigbookExample[[
See this \x[internal-cross-reference]{p}[awesome section].
]]

= Cross reference title inflection
{parent=internal-cross-reference}

A common usage pattern is that we want to use \x[header] titles in \x[x-full-argument][non-full] \x[internal-cross-reference]{p} as the definition of a concept without repeating the title, for example:
``
== Dog

Cute animal.

\x[cats][Cats] are its natural enemies.

== Cats

This is the natural enemy of a \x[dog][dog].

\x[dog][Dogs] are cute, but they are still the enemy.

One example of a cat is \x[felix-the-cat].

=== Felix the Cat

Felix is not really a \x[cats][cat], just a carton character.
``

However, word https://en.wikipedia.org/wiki/Inflection[inflection] makes it much harder to avoid retyping the definition again.

For example, in the previous example, without any further intelligent behaviour we would be forced to re-type `\x[dog][dog]` instead of the desired `\x[dog]`.

OurBigBook can take care of some inflection cases for you.

For capitalization, both headers and cross reference macros have the `c` \x[boolean-argument] which stands for "capitalized":
* for headers, `c` means that the header title has fixed capitalization as given in the title, i.e.
* if the title has a capital first character, it will always show as a capital, as is the case for most https://en.wikipedia.org/wiki/Proper_noun[proper noun]
* if it is lower case, it will also always remain lower case, as is the case for some rare proper nouns, notably https://en.wikipedia.org/wiki/Arm_Holdings[the name of certain companies]

This means that for such headers, `c` in the `x` has no effect. Maybe we should give an error in that case. But lazy now, send PR.
* for cross reference macros, `c` means that the first letter of the title should be capitalized.

Using this option is required when you are starting a sentence with a non-proper noun.
Capitalization is handled by a \x[javascript-case-conversion].

For pluralization, cross reference macros have the `p` \x[boolean-argument] which stands for "pluralize":
* if given and true, this automatically pluralizes the last word of the target title by using the https://github.com/blakeembrey/pluralize library
* if given and false, automatically singularize
* if not given, don't change the number of elements
If your desired pluralization is any more complex than modifying the last word of the title, you must do it manually however.

With those rules in mind, the previous OurBigBook example can be written with less repetition as:
``
== Dog

Cute animal.

\x[cats]{c} are its natural enemies.

== Cats

This is the natural enemy of a \x[dog].

\x[dog]{p} are cute, but they are still the enemy.

One example of a cat is \x[Felix the Cat].

=== Felix the Cat
{c}

Felix is not really a \x[cats][cat], just a carton character.
``

If plural and capitalization don't handle your common desired inflections, you can also just create custom ones with the \x[h-synonym-argument].

Now for a live example for quick and dirty interactive testing.

= Cross reference title inflection example
{parent=cross-reference-title-inflection}

\OurbigbookExample[[
\x[inflection-example-not-proper]
]]

\OurbigbookExample[[
\x[inflection-example-not-proper]{c}
]]

\OurbigbookExample[[
\x[inflection-example-not-proper]{full}
]]

\OurbigbookExample[[
\x[inflection-example-proper]
]]

\OurbigbookExample[[
\x[inflection-example-proper]{c}
]]

\OurbigbookExample[[
\x[inflection-example-not-proper-lower]
]]

\OurbigbookExample[[
\x[inflection-example-not-proper-lower]{c}
]]

\OurbigbookExample[[
\x[inflection-example-proper-lower]
]]

\OurbigbookExample[[
\x[not-readme]
]]

\OurbigbookExample[[
\x[not-readme]{c}
]]

\OurbigbookExample[[
\x[inflection-example-not-proper]{p}
]]

\OurbigbookExample[[
\x[inflection-plural-examples]
]]

\OurbigbookExample[[
\x[inflection-plural-examples]{p}
]]

\OurbigbookExample[[
\x[inflection-plural-examples]{p=0}
]]

\OurbigbookExample[[
\x[inflection-plural-examples]{p=1}
]]

\OurbigbookExample[[
\x[not-the-readme-header-with-fixed-case]
]]

= Inflection example not-proper
{parent=cross-reference-title-inflection-example}

= Inflection example proper
{c}
{parent=cross-reference-title-inflection-example}

= inflection example not-proper lower
{parent=cross-reference-title-inflection-example}

= inflection example proper lower
{c}
{parent=cross-reference-title-inflection-example}

= Inflection plural examples
{parent=cross-reference-title-inflection-example}

= `\x` within `title` restrictions
{parent=internal-cross-reference}

If you use `\x` within a `title`, which most commonly happens for \x[image][image titles], that can generate complex dependencies between IDs, which would either be harder to implement, or lead to infinite recursion.

To prevent such problems, OurBigBook emits an error if you use an `\x` without content in the `title` of one of the following elements:
* any \x[header]. For example, the following gives an error:
``
= h1
{id=myh1}

== \x[myh1]
``

This could be solved by either adding a content to the reference:
``
= h1
{id=myh1}

== \x[myh1][mycontent]
``
or by adding an explicit ID to the header:
``
= h1
{id=myh1}

== \x[myh1]
{id=myh2}
``
* non-header (e.g. an \x[image]) that links to the title of another non-header

For non-headers, things are a bit more relaxed, and we can link to headers, e.g.:
``
= h1

\Image[myimg.jpg]
{title=my \x[h1].}
``
This is allowed because OurBigBook calculates IDs in two stages: first for all headers, and only later non non-headers.

What you cannot do is link to another image e.g.:
``
\Image[myimg.jpg]
{id=myimage1}
{title=My image 1.}

\Image[myimg.jpg]
{title=my \x[h1].}
``
and there the workaround are much the same as for headers: either explicitly set the cross reference content:
``
\Image[myimg.jpg]
{id=myimage1}
{title=My image 1.}

\Image[myimg.jpg]
{title=my \x[h1][My image 1].}
``
or explicitly set an ID:
``
\Image[myimg.jpg]
{id=myimage1}
{title=My image 1.}

\Image[myimg.jpg]
{id=myimage2}
{title=my \x[h1].}
``

While it is technically possible relax the above limitations and give an error only in case of loops, it would require a bit of extra work which we don't want to put in right now: https://github.com/cirosantilli/ourbigbook/issues/95[].

Furthermore, the above rules do not exclude infinite rendering loops, but OurBigBook detects such loops and gives a nice error message, this has been fixed at: https://github.com/cirosantilli/ourbigbook/issues/34

For example this would contain an infinite loop:
``
\Image[myimg.jpg]
{id=myimage1}
{title=\x[myimage2].}

\Image[myimg.jpg]
{id=myimage2}
{title=\x[myimage1].}
``

This infinite recursion is fundamentally not technically solved: the user has to manually break the loop by providing an `x` content explicitly, e.g. in either:
``
\Image[myimg.jpg]
{id=myimage1}
{title=\x[myimage2][my content 2].}

\Image[myimg.jpg]
{id=myimage2}
{title=\x[myimage1].}
``
or:
``
\Image[myimg.jpg]
{id=myimage1}
{title=\x[myimage2].}

\Image[myimg.jpg]
{id=myimage2}
{title=\x[myimage1][my content 1].}
``

A closely related limitation is the simplistic approach to \x[x-id-output-format].

= Internal cross file reference
{parent=internal-cross-reference}

Reference to the first header of another file:
\OurbigbookExample[[
\x[not-readme]
]]

Reference to a non-first header of another file:
\OurbigbookExample[[
\x[h2-in-not-the-readme]
]]

To make toplevel links cleaner,if target header is the very first element of the other page, then the link does not get a fragment, e.g.: `\x[not-readme]` rendered as:
``
``
and not:
``
``
while `\x[h2-in-not-the-readme]` is rendered with the fragment:
``
``

Reference to the first header of another file that is a second inclusion:
\OurbigbookExample[[
\x[included-by-not-readme]
]]

Reference to another header of another file, with \x[x-full-argument][`full`]:
\OurbigbookExample[[
\x[h2-in-not-the-readme]{full}.
]]
Note that when `full` is used with references in another file in \x[embed-includes][multi page mode], the number is not rendered as explained at: \x[x-full-argument-in-internal-cross-file-references]{full}.

Reference to an image in another file:
\OurbigbookExample[[
\x[image-not-readme-xi]{full}.
]]

Reference to an image in another file:
\OurbigbookExample[[
\x[image-figure-in-not-the-readme-without-explicit-id]{full}.
]]

Remember that the \x[the-toplevel-header][ID of the toplevel header] is automatically derived from its file name, that's why we have to use:
\OurbigbookExample[[
\x[not-readme]
]]
instead of:
``
\x[not-the-readme]
``

Reference to a subdirectory:
\OurbigbookExample[[
\x[subdir]

\x[subdir/h2]

\x[subdir/notindex]

\x[subdir/notindex-h2]
]]
Implemented at: https://github.com/cirosantilli/ourbigbook/issues/116

Reference to an internal header of another file: \x[h2-in-not-the-readme]. By default, That header ID gets prefixed by the ID of the top header.

When using \x[embed-includes] mode, the cross file references end up pointing to an ID inside the current HTML element, e.g.:
``

``
rather than:
``

``
This is why IDs must be unique for elements across all pages.

= Internal cross file reference internals
{parent=internal-cross-file-reference}
{title2=`db.sqlite3`}

= ID database
{c}
{synonym}

When running in Node.js, OurBigBook dumps the IDs of all processed files to a `out/db.sqlite3` file in \x[the-out-directory], and then reads from that file when IDs are needed.

When converting under a directory that contains \x[ourbigbook-json], `out/db.sqlite3` is placed inside the same directory as the `ourbigbook.json` file.

If there is no `ourbigbook.json` in parent directories, then `out/db.sqlite3` is placed in the current working directory.

These follows the principles described at: \x[the-current-working-directory-does-not-matter-when-there-is-a-ourbigbook-json].

`db.sqlite3` is not created or used when handling input from stdin.

When running in the browser, the same JavaScript API will send queries to the server instead of a local SQLite database.

To inspect the ID database to debug it, you can use:
``
sqlite3 out/db.sqlite3 .dump
``

It is often useful to dump a single table, e.g. to dump the `ids` table:
``
sqlite3 out/db.sqlite3 '.dump ids'
``
and one particularly important query is to dump a list of all known IDs:
``
sqlite3 out/db.sqlite3 'select id from ids'
``

You can force `ourbigbook` to not use the ID database with the \x[no-db] command line option

= Internal cross reference title link removal
{parent=internal-cross-file-reference}

If the target `title` argument contains a link from either another \x[internal-cross-reference]{p} or a regular \x[link][external hyperlink], OurBigBook automatically prevents that link from rendering as a link when no explicit body is given.

This is done because https://stackoverflow.com/questions/9882916/are-you-allowed-to-nest-a-link-inside-of-a-link[nested links are illegal in HTML], and the result would be confusing.

This use case is most common when dealing with media such as \x[image]{p}. For example in:
``
= afds

\x[image-aa-zxcv-lolol-bb]

== qwer

\Image[Tank_man_standing_in_front_of_some_tanks.jpg]
{title=aa \x[zxcv][zxcv] \a[http://example.com][lolol] bb}

== zxcv
``
the `\x[image-aa-zxcv-lolol-bb]` renders something like:
``
aa zxcv lolol bb
``
and not:
``
aa zxcv lolol bb
``

Live example:
\OurbigbookExample[[
This is a nice image: \x[image-aa-zxcv-lolol-bb].

\Image[Tank_man_standing_in_front_of_some_tanks.jpg]
{title=aa \x[internal-cross-reference-title-link-removal][zxcv] \a[http://example.com][lolol] bb}
]]

= `\x` arguments
{parent=internal-cross-reference}

= `\x` `c` argument
{parent=x-arguments}

Capitalizes the first letter of the target title.

For more details, see: \x[cross-reference-title-inflection]{full}.

= `\x` `child` argument
{parent=x-arguments}

Setting the `child` \x[boolean-argument] on a cross reference to a header as in:
``
\x[my-header]{child}
``
makes that header show up on the list of extra parents of the child.

This allows a section to have multiple parents, e.g. to include it into multiple categories. For example:
``
= Animal

== Mammal

=== Bat

=== Cat

== Flying animal

These animals fly:
* \x[bat]{child}

These animals don't fly:
* \x[cat]
``
would render something like:
``
= Animal

== Mammal

=== Bat (Parent section: Mammal)
(Tags: Flying animal)

=== Cat (Parent section: Mammal)

== Flying animal (Parent section: Animal)

These animals fly:
* \x[bat]

These animals don't fly:
* \x[cat]
``
so note how "Bat" has a list of tags including "Flying animal", but Cat does not, due to the `child`.

This property does not affect how the \x[table-of-contents][`\Toc`] is rendered. We could insert elements sections there multiple times, but it has the downside that browser Ctrl + F searches would hit the same thing multiple times on the table of contents, which might make finding things harder.
``
== My title{id=my-id}

Read this \x[my-id][amazing section].
``

If the second argument, the `content`, is not present, it expand to the header title, e.g.:
``
== My title{id=my-id}

Read this \x[my-id].
``
is the same as:
``
== My title{id=my-id}

Read this \x[my-id][My title].
``

A live demo can be seen at: \x[x-child-argument-demo].

Generally, a better alternative to this argument is to use \x[h-child-argument].

= Secondary children
{parent=x-child-argument}

The term refers to sections that have a parent/child relationship via either of the:
* \x[x-child-argument]
* \x[x-parent-argument]
* \x[h-child-argument]
rather than via the usual \x[header] hierarchy.

Secondary children show up for example on the \x[tagged] metadata section, but not on the \x[table-of-contents], which is what the header hierarchy already shows.

Secondary children are normally basically used as "tags": a header such as `Bat` can be a direct child of `Mammal`, and a secondary child of `Flying animal`, or vice versa. Both `Mammal` and `Flying animal` are then basically ancestors. But we have to chose one main ancestor as "the parent", and other secondary ancestors will be seen as tags.

= `\x` `child` argument demo
{parent=x-child-argument}
{scope}

= Animal
{parent=x-child-argument-demo}

= Ant
{parent=animal}

= Cow
{parent=animal}

Oh, and cows are also \x[mammal]{parent}{p}.

= Mammal
{parent=animal}

= Bat
{parent=mammal}

= Cat
{parent=mammal}

= Flying animal
{parent=animal}

\x[bat]{child}{c}{p} can fly.

But \x[cat]{p} can't.

= `\x` `parent` argument
{parent=x-child-argument}

The `parent` argument is exactly like the \x[x-child-argument], but it reverses the direction of the parent/child relation.

= `\x` `full` argument
{parent=x-arguments}

To also show the section auto-generated number as in "Section X.Y My title" we add the optional `{full}` \x[boolean-argument] to the cross reference, for example:
\OurbigbookExample[[
\x[x-full-argument]{full}.
]]

`{full}` is not needed for cross references to most macros besides \x[header]{p}, which use `full` by default as seen by the `default_x_style_full` macro property in \x[help-macros]. This is for example the case for \x[image]{p}. You can force this to be disabled with `{full=0}`:
\OurbigbookExample[[
Compare \x[image-my-test-image]{full=0} vs \x[image-my-test-image]{full=1}.
]]

= `\x` `full` argument in internal cross file references
{parent=x-full-argument}

For example in the following \x[internal-cross-file-reference]:
\OurbigbookExample[[
\x[h2-in-not-the-readme]{full}.
]]
we get just something like:
``
Section "h2 in not the readme"
``
instead of:
``
Section 1.2 "h2 in not the readme"
``
This is because the number "Section 1.2" might already have been used in the current page, leading to confusion.

= `\x` `p` argument
{parent=x-arguments}

Pluralizes or singularizes the last word of the target title.

For more details, see: \x[cross-reference-title-inflection]{full}.

= `\x` `ref` argument
{parent=x-arguments}

The `ref` argument of `\x` marks the link as reference, e.g.:
``
Trump said this and that.\x[donald-trump-access-hollywood-tape]{ref}

= Donald Trump Access Hollywood tape
``
renders something like:
``
Trump said this and that.*
``

This could currently be replicated without `ref` by just using:
``
Trump said this and that.\x[donald-trump-access-hollywood-tape][*]
``
but later on we might add more precise reference fields like the page of a book or date fetched as Wikipedia supports.

Implemented at: https://github.com/cirosantilli/ourbigbook/issues/137

= OurBigBook Markup syntax
{c}
{parent=ourbigbook-markup}

= Insane macro shortcuts
{parent=ourbigbook-markup-syntax}

= Insane syntax
{synonym}

= Insane
{synonym}

Certain commonly used macros have insane macro shortcuts that do not start with backslash (`\`).

Originally, \x[design-goals][Ciro wanted to avoid those], but they just feel too good to avoid.

Every insane syntax does however have an equivalent sane syntax.

The style recommendation is: use the insane version which is shorter, unless you have a specific reason to use the sane version.

= Macros with insane shortcut
{parent=insane-macro-shortcuts}

* \x[paragraph]{child}{full}: `\n\n` (double newline)
* \x[link]{child}{full}: `a http://example.com b` (space followed by `http://`)
* \x[mathematics]{child}{full}: `$`, described at: \x[insane-code-and-math-shortcuts]
* \x[code-block]{child}{full}: \c[[`]], described at: \x[insane-code-and-math-shortcuts]
* \x[list]{child}{full}: `* ` and indentation
* \x[table]{child}{full}: `|| `, `| ` and indentation

= Insane code and math shortcuts
{parent=macros-with-insane-shortcut}

The insane code and math shortcuts work very analogously and are therefore described together in this section.

The insane inline code syntax:
\OurbigbookExample[[
a `b c` d
]]
and is equivalent to the sane:
``
a \c[[b c]] d
``

The insane block code:
\OurbigbookExample[[
a

``
b c
``

d
]]
and is equivalent to the sane:
``
a

\C[[
b c
]]

d
``

= Insane macro shortcut extra arguments
{parent=macros-with-insane-shortcut}

Insane arguments always work by abbreviating:
* the macro name
* one or more of its positional arguments, which are fixed as either \x[literal-arguments][literal or non-literal] for a given insane construct
This means that you can add further arguments as usual.

For example, an insane code block with an id can be written as:
``
a `b c`{id=ef} g
``
because that is the same as:
\OurbigbookExample[[
a \c[b c]{id=ef} g
]]
So we see that the `b c` argument is the very first argument of `\c`.

Extra arguments must come after the insane opening, e.g. the following does not work:
``
a {id=ef}`b c` g
``

This restriction things easy to parse for humans and machines alike.

= Escapes in insane macro shortcuts
{parent=macros-with-insane-shortcut}

Literal backticks and dollar signs can be produced witha backslash escape as in:
\OurbigbookExample[[
a \` \$ b
]]

It is not possible to escape backticks (\c[[`]]) inside an insane inline code, or dollar signs (`$`) in insane math.

The design reason for that is because multiple backticks produce block code.

The upside is that then you don't have to escape anything else, e.g. backslashes (`\`) are rendered literally.

The only way to do it is to use the sane syntax instead:
\OurbigbookExample[[[
a \c[[b ` c]] d

a \m[[\sqrt{\$4}]] d
]]]

Within block code and math, you can just add more separators:
\OurbigbookExample[[
```
code with two backticks
``
nice
```
]]

= Macro argument syntax
{parent=ourbigbook-markup-syntax}

= Positional vs named arguments
{parent=macro-argument-syntax}
{title2=`[...]` vs `{key=...}`}

Every argument in OurBigBook is either positional or named.

For example, in a \x[header] definition with an ID:
``
= My asdf
{id=asdf qwer}
{scope}
``
which is equivalent to the \x[insane-macro-shortcuts][sane] version:
``
\H[1][My asdf]
{id=asdf qwer}
{scope}
``
we have:
* two positional argument: `[1]` and `[My asdf]`. Those are surrounded by square brackets `[]` and have no name
* two named arguments: `{id=asdf qwer}` and `{scope}`.

The first one has name `id`, followed by the separator `=`, followed by the value `asdf qwer`.

The separator `=` always is optional. If not given, it is equivalent to an empty value, e.g.:
``
{id=}
``
is the same as:
``
{id}
``

You can determine if a macro is positional or named by using \x[help-macros]. Its output contains something like:
``
"h": {
"name": "h",
"positional_args": [
{
"name": "level"
},
{
"name": "content"
}
],
"named_args": {
"id": {
"name": "id"
}
"scope": {
"name": "scope"
}
},
``
and so we see that `level` and `content` are positional arguments, and `id` and `scope` are named arguments.

Generally, positional arguments are few (otherwise it would be hard to know which is which is which), and are almost always used for a given element so that they save us from typing the name too many times.

The order of positional arguments must of course be fixed, but named arguments can go anywhere. We can even mix positional and named arguments however we want, although this is not advised for clarity.

The following are therefore all equivalent:
``
\H[1][My asdf]{id=asdf qwer}{scope}
\H[1][My asdf]{scope}{id=asdf qwer}
\H{id=asdf qwer}{scope}[1][My asdf]
\H{scope}[1]{id=asdf qwer}[My asdf]
``

Just like named arguments, positional arguments are never mandatory.

= Positional argument
{parent=positional-vs-named-arguments}

See: \x[positional-vs-named-arguments]{full}.

= Positional argument default values
{parent=positional-argument}

Most positional arguments will default to an empty string if not given.

However, some positional arguments can have special effects if not given.

For example, an anchor with the first positional argument present (the URL), but not the second positional argument (the link text) as in:
\OurbigbookExample[[
\a[http://example.com]
]]
has the special effect of generating automatic links as in:
``
\a[http://example.com][http://example.com]
``

This can be contrasted with named arguments, for which there is always a default value, notably for \x[boolean-argument]{p}.

See also: \x[link]{full}.

= Mandatory positional arguments
{parent=positional-argument}

Some positional arguments are required, and if not given OurBigBook reports an error and does not render the node.

This is for example the `level` of a \x[header].

These arguments marked with the `mandatory: true` \x[help-macros] argument property.

= Named argument
{parent=positional-vs-named-arguments}

See: \x[positional-vs-named-arguments]{full}.

= Boolean argument
{parent=macro-argument-syntax}
{child=a-relative-argument}
{child=h-child-argument}
{child=h-numbered-argument}
{child=h-splitdefault-argument}
{child=x-c-argument}
{child=x-p-argument}
{child=x-ref-argument}

To also show the section auto-generated number as in "Section X.Y My title" we add the optional `{full}` \x[boolean-argument] to the cross reference, for example:

Name arguments marked in \x[help-macros] as `boolean: true` must either:
* take no value and no `=` sign, in which case the value is implicitly set to `1`
* take value exactly `0` or `1`
* not be given, in which case a custom per-macro default is used. Tha value is the `default` from \x[help-macros], or `0` if such default is not given

For example, \x[x-full-argument][the `full` argument] of \x[internal-cross-reference]{p} is correctly written as:
\OurbigbookExample[[
\x[boolean-argument]{full}
]]
without the `=` sign, or equivalently:
\OurbigbookExample[[
\x[boolean-argument]{full=1}
]]
The `full=0` version is useful in the case of reference targets that unlike \x[header]{p} expand the title on the cross reference by default, e.g. \x[image]{p}:
\OurbigbookExample[[
\x[boolean-argument]{full=1}
]]

The name "boolean argument" is given by analogy to the https://stackoverflow.com/questions/16109358/what-is-the-correct-readonly-attribute-syntax-for-input-text-elements/24588427#24588427["boolean attribute" concept in HTML5].

= JavaScript interface for arguments
{c}
{parent=macro-argument-syntax}

The JavaScript interface sees arguments as follows:
``
function macro_name(args)
``
where args is a dict such that:
* optional arguments have the key/value pairs explicitly given on the call
* mandatory arguments have a key documented by the API, and the value on the call.

For example, the link API names its arguments `href` and `text`.

= Literal arguments
{title2=`[[...]]` and `{{key=...}}`}
{parent=macro-argument-syntax}

Arguments that are opened with more than one square brackets `[` or curly braces `{` are literal arguments.

In literal arguments, OurBigBook is not parsed, and the entire argument is considered as text until a corresponding close with the same number of characters.

Therefore, you cannot have nested content, but it makes it extremely convenient to write \x[code-block]{p} or \x[mathematics].

For example, a multiline code block with double open and double close square brackets inside can be enclosed in triple square brackets:
\OurbigbookExample[[[
A literal argument looks like this in OurBigBook:

\C[[
\C[
A multiline

code block.
]
]]

And another paragraph.
]]]

The same works for inline code:
\OurbigbookExample[[[
The program \c[[puts("]");]] is very complex.
]]]

Within literal blocks, only one thing can be escaped with backslashes are:
* leading open square bracket `[`
* trailing close square bracket `]`

The rule is that:
* if the first character of a literal argument is a sequence of backslashes (`\`), and it is followed by another argument open character (e.g. `[`, remove the first `\` and treat the other characters as regular text
* if the last character of a literal argument is a `\`, ignore it and treat the following closing character (e.g. `]`) as regular text

See the following open input/output pairs:
``
\c[[\ b]]
\ b

\c[[\a b]]
\a b

\c[[\[ b]]
[ b

\c[[\\[ b]]
\[ b

\c[[\\\[ b]]
\\[ b
``
and close examples:
``
\c[[a \]]
a \

\c[[a \]]]
a ]

\c[[a \\]]]
a \]
``

= Argument leading newline removal
{parent=macro-argument-syntax}

If the very first character of an argument is a newline, then that character is ignored if it would be part of a regular plaintext node.

For example:
``
\C[[
a

b
]]
``
generates something like:
``
a

b

``
instead of:
``

a

b

``
This is extremely convenient to improve the readability of code blocks and similar constructs.

The newline is however considered if it would be part of some \x[insane-macro-shortcuts]{p=0}. For example, we can start an \x[list][insane list] inside a \x[quotation]{p} as in:
\OurbigbookExample[[
\Q[
* a
* b
]
]]
where the insane list requires a leading newline `\n* ` to work. That newline is not ignored, even though it comes immediately after the `\Q[` opening.

= Argument newlines between arguments removal
{parent=macro-argument-syntax}

The macro name and the first argument, and two consecutive arguments, can be optionally separated by exactly one newline character, e.g.:
``
\H[2]
{scope}
[Design goals]
``
is equivalent to:
``
\H[2]{scope}[Design goals]
``
and this non-recommended mixed style:
``
\H[2]{scope}
[Design goals]
``
This allows to greatly improve the readability of long argument lists by having them one per line.

There is one exception to this however: inside an \x[header][insane header], any newline is interpreted as the end of the insane header. This is why the following works as expected:
``
== My header 2 `some code`
{id=asdf}
``
and the `id` gets assigned to the header rather than the trailing code element.

= Escape characters
{parent=macro-argument-syntax}

For \x[literal-arguments][non-literal macro arguments], you have to use a backslash to escape:
* `\`: backslashes start macros
* `\` and `\`: open and close \x[positional-vs-named-arguments][positional macro arguments]
* `\` and `\`: open and close \x[positional-vs-named-arguments][optional macro arguments]
* `$` (dollar sign): \x[insane-macro-shortcuts][insane macro shortcut] for \x[mathematics]
* \c[[`]] (backtick): \x[insane-macro-shortcuts][insane macro shortcut] for \x[code-block]{p}

The escape rules for literal arguments are described at: \x[literal-arguments]{full}.

This is good for short arguments of regular text, but for longer blocks like \x[code-block]{p} or \x[mathematics], you may want to use \x[literal-arguments]

= Macro argument property
{parent=macro-argument-syntax}

= `remove_whitespace_children`
{parent=macro-argument-property}

In HTML, certain elements such as `