should setFocus and toggle be dynamic?

 
Right now, setFocus and toggle both work by using an ID. I propose
adding a "ref" attribute to allow them to compute this ID via XPath
expression. The use case is to toggle a switch/case dynamically or
transfer focus dynamically.
 
For example, you have a form taking a purchase order and the person can
pay by Credit Card, Check, or PayPal. Based on a <selectOne>, the person
choses their payment method, you would then like to <toggle> 3 different
UIs based on the selection value.
 
-Ray