FCKEditor

FCKEditor is a plug-in GUI editor for web applications, implemented in CSS and JavaScript and integrated in RT 3.8. It emits XHTML blocks for transaction bodies. RT sends mail for such transactions using the MIME text/plain type and a Markdown/SEText markup that is human-readable.

By default, FCKEditor is available to RT users, but its presence is not immediately obvious. You can make the default behavior to NOT use it with:

Set($MessageBoxRichText, 0);

However, users can still turn it back on in their own individual preferences.