```text
    Alice <alice@example.org>
    |
    | Authorization (depth: 1, amount: 120),
    | Regular expression: some.org
    v
    Bob <bob@example.org>/<bob@some.org>/<bob@other.org>
   /                   \
  / Certification       \ Certification
v                        v
Carol <carol@some.org>   Dave <dave@other.org>
```

Alice delegates to Bob via a certification on "<bob@example.org>", but
only for "some.org".  Bob's email address is not in some.org, but that
shouldn't matter.  He should still be able to introduce Carol, because
her email is in "some.org", and his own self-signed user ID,
"<bob@some.org>".
