+ width, height e.g in tables, images
 + anchors need to be <a id="..." instead of <a name="
 + img must have an alt attribute, even if it is empty (omitting is not
allowed)
 + one thing that was already mentioned, the proper nesting of elements:
there are no div elemtents allowed inside p elements (validator.w3.org says:
"Error: element "div" not allowed here; possible cause is an inline element
containing a block-level element"),
so we have to replace nearly all p elements by div elements, one exception
would be the simpara-->p transformation, which seems to be ok.
this are the first things that have come into mind, so this list has to be
filled.