The default behavior of a query in lwreg is to standardize the query molecule, calculate the default registration hash, and then use that to query the table with molecule hashes. This returns the molregno of the matching entry or None if no match is found. It is also possible to specify which layers of the registration hash should be used. Depending on which layers are selected, this allows querying for, for example, registered molecules that are tautomers or stereoisomers of the query. When the system is in registerConformers mode and the query molecule has a conformer, the conformer hash is calculated for the query molecule and used to query the conformer_hash table. Matches are returned as (molregno, conf_id) tuples.