Variables
Like any programming language GML contains variables. Variables are memory
locations that store information. They have a name so that you can refer
to them. A variable in GML can store either a real number or a string.
Variables do not need to be declared like in many other languages. There
are a large number of built-in variables. Some are general, like
mouse_x and
mouse_y that indicate the current mouse
position, while all others are local to the object instance for which we
execute the program, like x and y that indicate the current position of
the instance. A variable has a name that must start with a letter and can
contain only letters, numbers, and the underscore symbol '_'. (The maximal
length is 64 symbols.) When you use a new variable it is local to the
current instance and is not known in programs for other instances (even of
the same object). You can though refer to variables in other instances;
see below.