[tei-council] confusion about TEI at version and teiCorpus at version

[Kevin Hawkins]

Shouldn't the datatype TEI at version and teiCorpus at version (but not 
unicodeName at version) be xsd:anyURI so that these two work like @source 
(in att.readFrom)?  If so, should I submit this as as bug report or a 
feature request?

But more generally, what purpose do TEI at version and teiCorpus at version 
serve?  We say that people should use a customization of the TEI, so in 
what way would a given TEI document be valid against a "version number 
of the TEI Guidelines" (as defined for TEI at version) or "the TEI scheme" 
(as defined for teiCorpus at version)?