XML mention domain

The XML-mention domain elements are used to describe and document XML document types and applications. They also can enable typographic styling, search and retrieval, and automatic indexing for XML constructs.

Note (non-normative):

Although the original XML 1.0 Recommendation reserved element names beginning with "xml" or "XML" for the use of the XML standard itself, the subsequent introduction of namespaces made the restriction unnecessary. The restriction was formally removed in the XML 1.0 Fifth Edition Specification Errata. The OASIS DITA Technical Committee acknowledges this revised policy in its use of the prefix "xml" for the XML mention domain.