This function returns whether a given variable is a boolean (true ior false) or not. In some cases you want to check and see if a variable in GameMaker Studio 2 holds a boolean value, and that's when you would use this function.
Argument Description n The argument to check.
global.Sound = val;
global.Sound = true;
The above code checks the variable "val" to see if it is a real number and if it is it then uses it to set a global variable.