There is a DTD, doc type definition that does enforce which XML entities and properties are allowed.
I was thinking you meant an XML property as opposed to a TripleA <property> tag. In XML, a property is typically a value after a tag, eg: <tag property=123>
When parsing in an enforcing mode the DTD defines which properties are valid and which are not.
Though you are right about property name values. An unrecognized one would go unused. EG: <property name='not-recognized'>