gistfile1.js

A.mix(
		YUI.AUI.defaults.FormValidator.STRINGS,
		{
			customRule: 'Type the number 55.',
			anotherRule: 'Message for another rule'
		},
		true
	);

	A.mix(
		YUI.AUI.defaults.FormValidator.RULES,
		{
			customRule: function(val, fieldNode, ruleValue) {
				return (val == 55);
			},

			anotherRule: function(val, fieldNode, ruleValue) {
				return (val == 'another');
			}
		},
		true
	);