Add some expression documentation
Add some expression documentation

pombredanne/pyeda,karissa/pyeda,cjdrake/pyeda,sschnug/pyeda,sschnug/pyeda,karissa/pyeda,karissa/pyeda,cjdrake/pyeda,GtTmy/pyeda,cjdrake/pyeda,pombredanne/pyeda,sschnug/pyeda,GtTmy/pyeda,GtTmy/pyeda,pombredanne/pyeda