custom container control (IFRAME) that adjusts it height after dynamic client-side content changes?

[TR]

When an IFRAME contains dynamic content (e.g. a DIV is made visible, or
hidden, by client-side script) its height needs to be adjusted. I've seen
examples of how to do this onLoad, but when client-side script is causing
the content to grow (or shrink) the onLoad event doesn't fire, of course.

Is there a robust custom control which hosts an IFRAME which can calculate
the height of its contents and adjust its own height accordingly, whenever
it is asked to do so? An IFRAME is needed because we want an aspx page to be
able to nest other aspx pages.

Or is there a client-side way to cause the iframe's
contentWindow.document.body.scrollHeight property to be recalculated?

Thanks for advice, suggestions.
TR