xml:id Requirements

Since XML 1.0, the ability of processors to identify an XML element by an explicit identifier ("IDness") has depended upon validation. Both DTDs and XML Schema have mechanisms to identify the structures containing unique identifiers. But neither XML Schema nor DTDs are required by all processors. A common processor type does not perform validation, nor fetch external resources for the purpose of acertaining whether the document contains unique identifiers. This document sets out the requirements for a mechanism for determining "IDness" applicable to all classes of XML processors.