Add doc for contains function
Add doc for contains function

jacwright/prosemirror,adrianheine/prosemirror,kiejo/prosemirror,salzhrani/prosemirror,tzuhsiulin/prosemirror,mattberkowitz/prosemirror,salzhrani/prosemirror,jacwright/prosemirror,kiejo/prosemirror,kiejo/prosemirror,tzuhsiulin/prosemirror,mattberkowitz/prosemirror,adrianheine/prosemirror,tzuhsiulin/prosemirror,salzhrani/prosemirror,adrianheine/prosemirror