Honestly, the most difficult part for me has been just displaying the content efficiently, and scrolling accordingly. The other difficult part (that I was able to do) is creating the routines for moving around memory to insert/delete/overwrite. All the fancy stuff like tokenizing (i.e., turning the text "Line(" into the "Line(" token) and re-tokenizing (i.e. displaying "WLine(" as "WhiteLine(") are pretty easy, but tedious. Making menus is difficult, but I already have some pretty general-purpose menu routines, so that is also just tedious.

Hmm so it was like a road block when creating the mem editing routines. All I'm thinking about right now is how Mimas works. You can choose what type of assembly program to compile for. Why not just make it so that you can just input the type of program and when you type a word it tokenizes it accordingly? Like a source editor/compiler. That would save the having to use the OS Tokens.(My main thought here is with Grammer. I don't know how hard it would be to imput the tokens according to text into an actual basic program :| )

I found the edge cases the worst. There are so many different special scenarios that break your nice logic. Ignoring those, a program editor is quite easy to write. I could probably whip up a fully functional editor is 2 days if I didn't have those as a roadblock.