9.1.7 Unknown Relationships

All relationships not defined within ISO/IEC 29500 are considered unknown relationships. Unknown relationships are permitted within an Office Open XML document provided that they conform to relationship markup guidelines as defined by the OPC specification. Specifically:

• Conforming consumers shall not fail to load a document containing unknown relationships.

• Conforming producers that are also consumers can, but are not required to, roundtrip and preserve unknown relationships and their target parts.

It is a requirement of ISO/IEC 29500 that dynamic extension mechanisms, such as scripting languages and macro mechanisms, shall use, for the executable parts, the correct content types, and shall not use any of the content types already defined in ISO/IEC 29500.

[Guidance: This subclause defines the general behavior for the consumption of unknown relationships. A conforming producer that wishes to store custom business data in an Office Open XML document should use instead the known relationship type for Custom XML Data Storage parts, as defined in 15.2.4. end guidance]