This namespace defines the set of properties that may be associated with one or more custom XML parts within an Office Open XML document. A custom XML part is a part within an Office Open XML document, that contains arbitrary custom XML markup not necessarily defined by this Office Open XML Standard, and which is kept independent from the presentation-specific markup within the package.

[Rationale: It is often necessary to include custom XML semantics with an Office Open XML document, to store a complex set of properties (e.g., a document management system's metadata) along with the file. This mechanism allows this custom XML to be stored in the document in a way that is independent of the type of document and separate from the presentation markup—only the custom XML is stored in this part. end rationale]

The properties that can be applied to a custom XML part are:

• A part ID

• (optionally) One or more associated custom XML schemas