You can open GMS, you just shouldn’t open the specific resources in GMS if you’ll be opening them in GMEdit.
If the cache is cleared, the GMS1 performs an autosave when running the game, even if nothing has been changed through it. It's not a big risk, but a "compiler only" mode via command line or etc would make GMS1 perfect for use with GMEdit (but why help if we can make it difficult, right YoYo Games? xD).
I don’t know what “doesn’t even compare variable names means”, but GMEdit has a lot of type checking and JSDoc lines that can warn you about mistyped variables.
Sorry my English is bad. I was saying that having autocompletion in GMEdit is already a giant step when GMS1 doesn't even have it for variable names.
GRAPHIC_OPTIONS = 7; // ... menuState = GRAPHIC_OPTIONS;
Again, my English is bad and you apparently didn't understand it very well. If I had a list of behaviors for a state machine and wanted to label them with strings, eg:
myState = "idle";
And my list of behaviors like:
"walk", "run", "shot", "swim", "roll", "pick", "drop", "attack", "talk"...
At some point in the code I want to set the state to catch, so I do myState="... well, I don't remember if I used "catch" or "pick" or even "take", and since it's a string I won't have an autocomplete hint.
Obviously, this example is very simplistic, we are talking about much more complex contexts and labels composed of 3 or 4 words. Enums can be a good alternative, but I have to go back to the point where I declared it to feed the list with new labels, whereas in autocomplete, I just have to type it once to make it available.
Anyway, I just speculated a possible feature similar to autocomplete in Excel cells. I understand that there is no "cost x benefit" to implement it =/