Checks if a mouse button is down.

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#### Syntax:
```lua
bool = isMDown(b)
```

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#### Arguments:

* **<b\> (Number)**: The button to check, 1 for left mouse button, 2 for right mouse button, 3 for middle mouse button.

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#### Returns:

* **bool (Boolean)**: True if mouse button is down, false if not.

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##### See also:

* [getMPos()](getMPos.md)