Elaborate re-use of existing standard identifiers in the bound 'extra'-field.

[titusz]

If cross-sector clustering of the Meta-ID is not required, then users may add existing identifiers to the bound “extra”-field for Meta-ID generation. Encoding existing identifiers into the Meta-ID at random is discouraged and does not provide any practical value besides disambiguation from other similar Meta-IDs. If at all, specific industries should first agree about such conventions. Ideally such conventions should also be documented by the ISCC standard.