Halliday & Matthiessen (2014: 286):
… the [decoding] type of ‘identifying’ clause where the Identifier is the Value (that is, the identity is given by function) is intermediate between the attributive and the other [encoding] type of ‘identifying’, the one where the Identifier is the Token (identity is given by form):
Pat is rich Attribute attributive
Pat is the richest Identifier/Value decoding
the richest is Pat Identifier/Token encoding