GEdit uses GtkSourceView to find keywords and code enclosures in a text file and give them syntax highlighting for easier editing.
I need to create a custom language file that treats all text enclosed within triple brackets [[]] as highlighted, so any non-bracketed text can be easily seen.
The documentation is here:
Please describe how to modify an existing .lang file (these are stored at /usr/share/gtksourceview-VERSION/language-specs on most systems. Describe how and why it works.