legal-entity-identifier

[HadleyKing]

@HadleyKing - I want to add https://www.gleif.org/en/about-lei/introducing-the-legal-entity-identifier-lei to the spec. This suggestion came from Frank at FDA. This is optional. But will help with the identifiers.

[HadleyKing]

For now this can be added as an Xref and referenced in the Usability Domain.
Need to find an example to demonstrate this.