nervermatch - value never match.
equal - field equal to the value.
notequal - field not equal to the value.
lessthanequal - field less than or equal to the value.
greaterthanequal - field greater than or equal to the value.
fieldexist - value is ignored if field exists.
fieldnotexist - value is ignored if field does not exist.
alwaysmatch - value always match.