Anyone have a recommendation for an editor like the WMD editor, but using MediaWiki markup instead of Markdown? Our site is already using MediaWiki markup but we want a slicker editor without changing markup completely.

Requirements include:

• live preview of formatted text underneath the markup you're typing
• a toolbar for common formatting (bold, italic, links, bullets, numbered-list, code, etc)
• keyboard shortcuts for each toolbar button (e.g. CTRL+B for bold)
• Undo/redo via keyboard shortcuts (CTRL+Z/CTRL+Y) or toolbar buttons
• works well in the usual set of popular browsers (including IE6!)
• open-source would be preferred

I've found a few options at http://www.mediawiki.org/wiki/WYSIWYG_editor, but all of these seem to be WYSIWYG editors which is not exactly what I want since full-on WYSIWYG editors tend to be bug-prone and complicate working at the markup level. Instead we want a plain-text markup editor with a client-side previewer, plus some UI niceties (toolbar, undo, keyboard shortcuts) to make editing markup easier.