Validar RFC y CURP

[Madian]

La siguiente funcion valida la CURP
<script>
function _validarcurp(txt){
if ( ! txt.value.match(/[a-zA-Z]{4,4}[0-9]{6}[a-zA-Z]{6,6}[0-9]{2}/) )
{
return false
}
else
{
return true;
}
}

</script>
o esta forma
<input onchange="if ( ! this.value.match(/[a-zA-Z]{4,4}[0-9]{6}[a-zA-Z]{6,6}[0-9]{2}/) ) { this.value = '' }">