RE: [xml-dev] What does "optional" mean?

["Costello, Roger L." <costello@mitre.org>]

> I would agree with David Carlisle.
> In schema,  "optional" doesn't mean ANY of the items you suggest.

Yes, I stand corrected. Despite my best efforts, how quickly and easily I fall into the trap of ascribing meaning to constructs in schemas.

Let me rephrase my question: 

       Why make one element mandatory 
      and another optional?

That is, what is it about some information that it is declared mandatory whereas another information is declared optional?

/Roger