Attribute: Source
When used in the <Identifer> element, it designates the organizational authority that established the unique identifier, e.g. ORCID or International Standard Name Identifier (ISNI). When used in the <OtherID> element, it identifies the source of the additional identifier associated with the record.
In <OtherID>
Source (NASA|KIE|PIP|POP|ARPL|CPC|IND|CPFH|CLML|NRCBL|NLM|QCIM) #REQUIRED
In <Identifier>
Source CDATA #REQUIRED