2.1.1725 Part 1 Section 188.8.131.52, ST_RelationshipId (Explicit Relationship ID)
a. The standard does not limit the length of the contents of the ST_RelationshipId simple type.
Office restricts the contents of this simple type to be at most 255 characters.
b. The standard states that the values of the ST_RelationshipId simple type are a restriction on the XML Schema string datatype.
Office defines this simple type as being a restriction on the XML Schema id datatype.