When creating a struct, it is possible to use certain built-in variables as member variable names, for example:
mystruct =
{
object_index : obj_Player,
speed : 3,
image_blend : c_red
}
However, only local and instance scope built-in variables can be used this way and assigned values as if they were regular struct member variables. Using global scope built-in variables is forbidden and will cause issues with your game. Below you can find a full list of these variables so that you know which ones to avoid.
The following built-in global variables are all available for use in your projects but cannot be used as struct member variables:
Apart from those global variables, there are also a number of obsolete built-in global variables that are unavailable due to the possibility of them being included in imported legacy products (GameMaker needs to reserve these variables so it can recognise them on import and flag them to be updated/removed):