7.4.3
Property names in GML
The fes:ValueReference element can used to specify the name of any property of an object whose value shall be tested by a predicate in a filter expression. For services that implement this International Standard and use GML (see ISO 19136), property names shall be encoded using XML elements as described in the Extensible Markup Language (XML) 1.0 (see W3C XML) specification. In addition, GML property names may be qualified with a namespace, in which case the name shall conform to the Namespaces in XML (as given in W3C XML Namespaces) specification. The following definition is taken from Clauses 2 and 3 of W3C XML Namespaces:
Names and Tokens