kMDItemPath: absolute path.
kMDItemFSName: basename.
kMDItemFSSize: size in bytes.
kMDItemDisplayName: display name.
kMDItemContentType: UTI.
kMDItemContentTypeTree: UTI and parent UTIs.
kMDItemKind: a localized name for the content type.
kMDItemFSContentChangeDate: modification time.
kMDItemFSCreationDate: creation time.
kMDItemLastUsedDate: date last opened.
kMDItemDateAdded: date added.
kMDItemFinderComment: Spotlight comment.
kMDItemTextContent: plain text content of for example text, HTML, or PDF files.
kMDItemDurationSeconds: for example the duration of an audio or video file.
kMDItemTitle: for example the title of a webloc, PDF, or MP3 file.
kMDItemURL: for example the URL of a webloc file.
kMDItemWhereFroms: the URL or URLs that a file was downloaded from.
kMDItemUserTags: tags in 10.9 and later.
kMDItemAuthors: for example the artist of an MP3 file.
mdfind 'kMDItemTextContent="*expose*"cd' # search for files whose content matches `expose` ignoring case and diacritics
mdfind 'kMDItemTextContent="*search phrase*"c' -onlyin ~/Library/Caches/Metadata/Safari/History