http://www.xulplanet.com/tutorials/xultu/advrules.html http://www.xulplanet.com/reference/elemref/ref_binding.html Should be contained within a bindings element. A binding is used to bind a variable to a node. Like the triple element in syntax, it can be used to bind a particular property of a matched node to a particular variable name. That name can then be used within the action of a rule. The object of a binding. It can be a variable reference, an RDF resource URI, or an RDF literal value. The predicate or property to match. This must be a URI of the property. The subject of a binding. It can be a variable reference or an RDF resource URI.