This is a gtksourceview language definition that gives Constraint Grammar syntax highlighting in editors like Gedit.
To use:
git clone https://github.com/goavki/syntxfile_gedit_CG/
cd syntxfile_gedit_cg
mkdir -p ~/.local/share/gtksourceview-3.0/language-specs/
cp rlx.lang ~/.local/share/gtksourceview-3.0/language-specs/Now any file ending in .rlx or .cg3 will get CG syntax highlighting in Gedit.