Need help creating custom MIME type for contextual text highlighting

I would like to save a plain text journal entry with a unique file extension. Goal is to see contextual highlighting like that of .html in Gedit; but with my custom comment flags highlighting lines, and a custom list of keywords highlighted.
If it only works in Gedit that would be okay. But a solution that applies to any text editor would be fantastic.
•Bullets surround a Question. Automatically displays in special color.•
Answers are in the standard color set. Keywords have some automatic emphasis.
Is this possible?

Pardon the abuse of the formatting tools available here. I have no idea where to begin with tags for this topic.

If you invent a new markup to use you cannot expect existing editors to know you did this.
Adding a MIME type does help add the code to support it to existing editors.

If you use a programmable editor you could add a mode to the editor to highlight your custom markup.

From my research I know I would have to define the behavior with an xml file. But this is only one piece of the puzzle.
I found a guide for custom applications that seemed promising. This was on gnome’s site, about adding custom MIME types. The directory structure for applications is different than the way text documents are handled. That guide was more about getting the icon to display correctly, rather than context highlighting / markup.
Somebody knows how to do this…