docs: function(propertyName) {
  		var compares = new clause.Where({});
  		compares[propertyName] = function(propA, propB) {
  			// prop a is probably true
  			propA = convertToBoolean(propA);
  			propB = convertToBoolean(propB);
  			var notA = !propA,
  				notB = !propB;
  			if( propA === notB && propB === notA ) {
  				return {
  					difference: !propB,
  					union: undefined
  				};
  			} else if(propA === undefined) {
  				return {
  					difference: !propB,
  					intersection: propB,
  					union: undefined
  				};
  			} else  if(propA === propB) {
  				return true;
  			}
  		};
  		return compares;
  	}