entity descriptors from multiple registrars

[Tom Scavo]

Suppose a deployment consumes metadata from multiple sources such that
its metadata store contains entity descriptors from multiple
registrars (i.e., federations). How does Shibboleth distinguish
metadata from different registrars?

For the IdP, I think I know the answer: Install the
mdrpi-match-idp-ext add-on on Shibboleth IdP 2.4 (or later):

https://github.com/ukf/mdrpi-match-idp-ext

What is the answer for the Shibboleth SP?

Thanks,

Tom