function clearText(field){
    if (field.defaultValue == field.value) field.value = '';
    else if (field.value == '') field.value = field.defaultValue;
}

function validarEmail(valor) {
	if (/^\w+([\.-]?\w+)*@\w+([\.-]?\w+)*(\.\w{2,4})+$/.test(valor)) return (true);
	else return (false);
}

function validarURL(url) { 
	var re=/^http:\/\/[a-zA-Z0-9-_:/.?&=]+$/; 
	return re.test(url); 
}