Read our guide on Regions for an explanation of these blocks.

Returns a Region of choice (whether an instance of one, an attribute or other form).
[REGION]

Returns true if the actor is inside the specified region.
isInRegion([ACTOR], [REGION])

Creates a rectangular region with the given location and size. Assign to a Region attribute (using the "Last Created Region" selection) to refer to it in the future.
createBoxRegion([NUMBER], [NUMBER], [NUMBER], [NUMBER]);

Creates a circular region with the given location and size. Assign to a Region attribute (using the "Last Created Region" selection) to refer to it in the future.
createCircularRegion([NUMBER], [NUMBER], [NUMBER]);

Deletes a region from the current scene. (It will return if you leave the scene and come back.)
removeRegion([REGION].getID());

Moves the region to the given point.
[REGION].setLocation([NUMBER], [NUMBER]);

Moves the region to the given actor's location using its origin point.
[REGION].follow([ACTOR]);

Resets the region to its original size.
[REGION].resetSize();

Sets the size of a circular region to the given diameter.
[REGION].setRegionDiameter([NUMBER]);

Sets the size of a box region to the given width and height.
[REGION].setRegionSize([NUMBER], [NUMBER]);

Gets the [X/Y] location of the region.
[REGION].getX()
[REGION].getY()
[REGION].getXCenter()
[REGION].getYCenter()

Gets the [Width/Height] of the region.
[REGION].getWidth()
[REGION].getHeight()