code: function(a, b, aParent, bParent, prop, compares, options){
  	var subsetCheck;
  	if( !(prop in aParent)) {
  		subsetCheck = "subsetB";
  	} else if(prop in bParent){
  		// property in a and b and not the same
  		return false;
  	}
  	if( !(prop in bParent) ) {
  		subsetCheck = "subsetA";
  	}
  	if(subsetCheck === "subsetB") {
  		options.result[prop] = b;
  	} else {
  		options.result[prop] = a;
  	}
  	return undefined;
  }
docs: only adds a or b to `options.result` if missing properties are always on the super set. {foo: "bar", "zed": "ted"} intersection {} -> {foo: "bar", "zed": "ted"}