This is the GtkSourceView syntax highlighting for Parsimonious grammars.
It can be installed in ~/.local/share/gtksourceview-3.0/language-specs, or /usr/local/share/gtksourceview-3.0/language-specs, or /usr/share/gtksourceview-3.0/language-specs.
WTFPL 2.0
See https://wiki.gnome.org/Projects/GtkSourceView and https://developer.gnome.org/gtksourceview/unstable/syntax-highlighting-reference.html for reference.