Dynamic Properties in Dynamic HTML (DHTML)
http://www.intranetjournal.com/articles/200005/dynamic_index.html

Gilbert-Baffoe, Nana
Intranet Journal

Abstract:

While experimenting with DHTML you may have ended up with a situation where you'd wanted to possibly have an element that has a width that's always the same as another element's height. On the other hand, you may have wanted to center an element in the middle of the page no matter what the width of the page was. All this is possible with the DHTML methods you've learned previously, but you will find that these scripts end up being unnecessarily long or complicated. That's why Dynamic Properties were introduced in IE 5.0. Dynamic Properties, as the name may indicate, means the ability to assign non-static dynamic values to properties.