Prive wrote:

> Why is border not an attribute of iframe in HTML 4.0?
> 
> Although most browsers support it, it is not a standard attribute of iframe
> and frameborder doesn't work.
   Because that would be another presentational attribute, and the 
popular browsers support many elements and attributes which are not 
standardised.  That is one reason for why they're called tag-soup browsers.

   If you look at the spec, most (unfortunately not all) of the 
presentational elements and attributes are deprecated.  Therefore, it 
was a good decision by the HTML 4 WG to not include it.

   If you want a border around an <iframe> use CSS, not the border 
attribute.
eg.
iframe {
     border: 1px solid black;
}

-- 
Lachlan Hunt