XML 1.0 notation simplification - ExternalID

I'm surprised by the fact that ExternalID [75] doesn't use PublicID [83].
If you substitute PublicID[83] into [75], you get:

 [75] ExternalID ::= 'SYSTEM' S SystemLiteral |
                     PublicID S SystemLiteral

That would be a simplification already.  But the following captures even
better my understanding of what's going on, since basically it says in
a clear way that a systemliteral is always allowed and that it is required
when there is no public id:

 [75] ExternalID ::= ( 'SYSTEM' | PublicID ) S SystemLiteral

Received on Monday, 20 April 1998 00:33:31 UTC