A few more comments...

Searhing by identifier: It may be useful to add 'uri' to the list of
accepted types. In particular, "info" URIs enompasses many types of
identifiers that aren't otherwise available through the listed
types. On the other hand, it is unlikely for a URI-based identifier to
conflict with an identifier of another type, so it may be more useful
to simply note that these types of identifiers should be searched
using dc.identifier with no type modifier.

What is the reasoning behind making some types of searches into
indices, and others into modifiers? If you compare Subject searches
with Date searches, there are several types of subjects listed as
indices, while the various types of dates are all specified by
modifiers. Why shouldn't there be a subject type modifer with values
'place', 'title', etc.? Why shouldn't there be an index called
bib.dateIssued? 

----- Ryan Scherle
----- Digital Library Program
----- Indiana University