iframe shim

Joe King : How to cover an IE windowed control (Select Box, ActiveX Object, etc.) with a DHTML layer.

Set up your IFRAME:

The src attribute is set with a useless JavaScript statement so that the IFRAME does not try to load a page (which you won't notice it doing, but it will be the cause for tripping the "Unsecured Items" message if you use it on a HTTPS page).

You can code your IFRAME as a static element on the page, or if you are going to be using more than one of them you may want to dynamically create them as required. The insertAdjacentHTML() method is good for that.

Now, all that is needed is to size the IFRAME according to the dimensions of your DIV, position it, place it one layer beneath the DIV in the zIndex order and make it "visible". The IFRAME's style object will allow you to do these tasks:

iframe.style.top
iframe.style.left
iframe.style.width
iframe.style.height
iframe.style.zIndex
iframe.style.display

What about transparency?

If the DIV has transparent areas, you'll want those areas to punch through the IFRAME to the page background. There are two ways you can make an IFRAME transparent. The one that works for this situation is to set the style object's filter property:

iframe.style.filter='progid:DXImageTransform.Microsoft.Alpha(style=0,opacity=0)';

This in effect makes the entire IFRAME transparent, but it will still block out the windowed controls. The other technique, which uses the IFRAME element's ALLOWTRANSPARENCY attribute, actually pertains to making the interior page background of the IFRAME transparent, so that any content inside the IFRAME can have transparency. However, this mode changes the nature of the IFRAME and it no longer serves our purpose for blocking out windowed controls.