Operation:
- set to
- add by
- subtract by
- multiply by
- divide by

Value of:
- Specified
- Random (range)
- a variable's name	(error then ignore)
- a variable's value	(error then ignore)
- EventName's
	- direction
	- Tile X
	- Tile Y
	- Pixel X
	- Pixel Y
	- Screen Pixel X
	- Screen Pixel Y

