Chris Waterson has authored a primer on XUL templates that describes the new rule based extension syntax.

XUL, Mozilla's XML User Interface Language, supports the ability to incorporate RDF graphs into its content model. This is done using XUL templates. Templates were recently enhanced to support a more sophisticated rule based processing model ala Prolog or OPS5. The new syntax allows the left hand side of a rule to match a specific RDF triple and supports the use of variables.

related stories:

• Enabling RDF-based inferencing in Mozilla.
• Fooling with XUL(article at XML.com).