Most people will find that the actual standard documentation itself is not very useful, since unfortunately the design of HL7 version 3 was, while conceptually very nimble and flexible, very constrained as to the expressivity of the presentation of the standard specification. In an over-zealous effort to make the standard specification formal and validated, the specification was released in diagrams and tables and databases and countless linked HTML pages but the documentation was not very user friendly. This is in large parts why the HL7 version 3 line of standards had collected some bad reputation and why HL7 itself had decided to start over from scratch, throwing away the superior model and going back to ad-hoc defined record formats where ad hoc data fields would be provided without systematic coherence. This may be an arguable statement, but the proof of this statement is that no useful PQ/CMC specification has been released let alone adopted which would even come close to being able to deal with molecular structures, reactions and process automation the way the SPL standard does, because these use cases are sacrificed on the altar of expediency.