So far as I can make out from the element descriptions at http://www.loc.gov/standards/mods/userguide/origininfo.html and related pages, there seems to be no way to express in MODS who the copyright holder of a work is -- which seems strange, as you CAN state the copyright date. Am I missing something? (The <publisher> element is not the answer here, as it's not at all unusual for the copyright to be held by someone other than the publisher -- the author, for example.)