The code (just a single file, twiki.lang) is open source (GPL, like gedit) and is hosted in a GitHub repository: https://github.com/darryllawson/gedit-twiki. The README available at that link has installation instructions and information on configuring the It's All Text! Firefox Add-on for use with gedit.
You might be wondering why TWiki syntax highlighting is useful? Here are a few reasons:
- By highlighting headings, document navigation is easier.
- By highlighting markup elements, it's easier to visualise formatting and detect syntax errors. For example, you'll know when you accidentally typed four spaces instead of the requisite three.
- By highlighting wiki words, you'll know straight away if you have typed a valid one, and it'll also be obvious when you need to escape one.