Basically it's an extension that allows you to automate stuff, where it will automatically replace certain keystrokes with phrases of your choice. Works very well for managing BBCode here.
For instance, if I wanted to create url tags, all I have to say is
[ur, and I get
[url=][/url].
Works for other things as well. For example, I made a set of Cyrillic characters have simple shortcuts.
Дд is typed
;d,d in my shortcuts, for instance.
I hope you find it useful.
Links:BBCode Usage & Greentext Shortcut