I have experience using this back when I worked for a startup that did distribution grid optimization. The specs are unfortunately useless in practice because while the terminology is standardized the actual use of each object and how to relate them is not.
Thus, every tool makes CIM documents slightly differently and there are no guarantees that a document created in one tool will be usable in another
That's why ENTSO-E has just completed a software vendor interoperability workshop. :-) And import/export/validation worked just fine for all participants.
Thus, every tool makes CIM documents slightly differently and there are no guarantees that a document created in one tool will be usable in another