"CQL is a formal language for representing queries to information retrieval systems such as web indexes, bibliographic catalogs and museum collection information." http://www.loc.gov/standards/sru/cql/.
The Search interface allows queries of the form:
Word1 and Word2 dc.title=Word1 and Word2 dc.identifier=^C 1.89"
There are only two searchable fields -- dc.title for title words, and dc.identifier for SUDOC identification numbers.