A bit of explanation: In the old days of table layouts, the width attribute of a dt element would declare the maximum width of that element only. In order to provide a minimum width, you'd insert a transparent 1x1px image and give it the appropriate width. This could be used both for flexible (min, max) layouts and rigid designs, where everything would be positioned by a system of pole-like transparent images, much like in a Dali painting.
Note on both frames and tables: Right from the beginning, you could declare width and height units in HTML both in percent and in absolute units, like "px". However, Netscape browsers used internally only percents! Meaning, if you you intended to span the entire width of a document, Netscape would convert your absolute units to percent and from this back to px (using integer math for speed) and you would end up with some rounding error depending on the width of the browser window, which could add up to a deviation of 4px or so. Which was, of course, a constant pain, when you intended to line up elements, like a logo on top and a structure with a navigation and a main content area in different colors below.
