This is a syntax highlighting file the GtkSourceView component used by text editors and integrated development environments such as GNOME Text Editor and GNOME Builder.

To install system-wide, copy the prql.xml file to:

/usr/share/gtksourceview-5/language-specs/

To install for the current user, copy the prql.xml file to:

~/.local/share/gtksourceview-5/language-specs/

To embed it in your GTK application using the GtkSourceView widget add it to a LanguageManager which you add to your Buffer.