minimal required - identifier, "creator", title, description, mediatype
anything accepted (and retrievable through meta.xml file stored on item's detail page)
subject(s) - what shows up under "Browse by subject/keyword" link for collection
identifier must be unique across all 7+ million items stored at I/A
file naming restrictions A-Z0-9._- no spaces, parenthesis, brackets pound signs allowed in file names
fields added by I/A - uploader, addeddate, publicdate, parent collections
extra fields are searchable but not returned in search results