This page covers GMEdit's support for the more antique GameMaker versions and custom languages that are equivalent to the said GM versions.

• GMEdit can edit code for scripts and objects
• GMEdit will try to open something reasonable for other resource types
• GMEdit cannot create/move/destroy resources because this isn't code that I can reuse from elsewhere

Rest assured, you'll want to have a "regular" IDE open alongside.

Same as usual, but with structure changes to make up for lack of var name = value.

Using ?arg assumes that you have a constant called undefined in your project.
Having undefined be chr(0) seems to be a reasonable idea in GM8.x.

Should work fine if you'll edit the script to not use buffers.

Some sort of conflict with other syntax extensions? I might look into it eventually.

Need to be able to create/destroy scripts for those!

Older GM versions have no ternary operators, short-circuit evaluations, and even no formal undefined type, so most of the other GMEdit extensions can't really work here.

These are exclusive to GM8.x

You can do

var a = 1, b = 2;

and this will turn into

var a, b; a = 1; b = 2;

Works for globalvar too!

Just like in the newer GM versions, you can use map[?key], list[|index] and grid[#x, y].

So

grid = ds_grid_create(4, 4);
grid[#1, 2] = "value";
map = ds_map_create();
map[?"key"] = grid[#1, 2];

will become

grid = ds_grid_create(4, 4);
ds_grid_set(grid, 1, 2, "value");
map = ds_map_create();
ds_map_set(map, "key", ds_grid_get(grid, 1, 2));

Helper functions come from this GML file that you can import by drag-and-dropping it onto GameMaker IDE window.