This is actually something I've started working on recently as a mod to 3.0.10 to include in a style that I'm building, but not as a button per se, as a tab link
Something like this:
While writing the message:
Previewing the message:
Used the livepreview mod code as base, but that is something that keeps refreshing all the time. This way it should only need to refresh after we click on the tab.
http://www.phpbb.com/customise/db/mod/l ... ew-t_99392
