[osis-core] How do we know which <work> within the <header> of <osisCorpus> is the THIS <work> for <osisCorpus>?

[Todd Tillinghast]

All,

How do we know which <work> within the <header> of <osisCorpus> is the
THIS <work> for <osisCorpus>?

What meaning do other <work> elements in the <header> of <osisCorpus>
have?  

Can they be used globally from within decendant elements of ANY
<osisText>?

Are "osisWork" attributes of <work> elements required to be unique
globally within the document of just within an individual <header>?

Patrick, these might be good things to document in the documentation
(what ever the "correct" answer is).

Todd