A quick test today using CodeMirror. The editor supports F11 fullscreen, tag highlighting, full search, code coloring, line numbering, visible tabs, highlights extra space, etc.

I currently only plan to have scripts written in PHP although the CodeMirror platform works for all kinds of languages if i want to expand in the future.

when editing scripts they will automatically save to the server as they are being edited (real time). the server will store the last 200 edits in a server side undo history and pass those back to Code Mirror if the local browser undo history hits 0 records. This will allow anyone to undo changes that were made some time ago using a different browser session.