I missed a lot while on vacation, this is looking amazing!
I can't wait to try it, great work as always!
I have a few suggestions:
-Ability to enable a specific key to restart script while on the page that runs it (any key or no key) because its annoying to do ctrl+left, escape, menu, enter, enter every time you want to restart it.
-Custom Libraries, with Adriweb's Better Lua API as a built in library. Also the ability to add other libraries of your own.
-Menu Items that are toggle based should have a checkmark next to them when turned on (checkmark character is in the character lib.. somewhere) EDIT: for things like font, write the current font next to it.
-Still waiting for that Standard Lib API guide
EDIT:
Okay, so I tried it out, and I have a few more suggestions/bug reports:
-Use of cursor.set() for selecting items in a dialog box, and for buttons
-Ability to click the X in the top right of the customize box
-Clicking outside of a dialog box is the equivalent of pressing escape
-The application that runs the script didn't work for me until I clicked on the page, after the first time it worked fine
-In the customization menu, draw a square with the current color of the item, next to the name of the item so you can tell what it is currently set to
-Ability to mark check boxes with cursor as well as buttons
-Customization of syntax separate from customization of other stuff
-Ability to save custom themes
-Ability to customize dialog box colors
Also, how did you use ctrl+M to select the line?
2nd EDIT: I just wrote a lot of stuff ^ I understand if you don't want to do any of it, or if its just too much. Just a few of my thoughts to improve. Can't wait for the next update!