How do I access current value of the field?

Not one saved, but one entered by user without hitting save.
Use case: On my configuration panel I have an input to enter URL of audio file, and a button that should play it. How do I access actual value of the input? Since you create iframe with about:blank URL, I can't access it's content directly.

Okay, found a workaround: in an event handler, you can use this.ownerDocument.documentElement to get the root element of the DOM tree, and work from there.