[XML-SIG] DOM documentation update

[Martin v. Loewis]

>   I'm not done with the DOM documentation, but I'm starting to see
> just how much of it there is to write!  ;-)
[...]
>   Please let me know if you find any errors or have any suggestions!

My suggestion would be: publish early, publish often. *Any* DOM
documentation (in particular the one that you had a month ago) would
be better than nothing. So I'd rather see a copy of today's version of
your documentation show up on python.org tomorrow, than wait until
next year before I can point people to DOM documentation.

As for the presentation itself: As I mentioned earlier, publishing the
IDL would have the advantage of documenting the type. In the current
document, the type is not stated for:

parentNode, nodeName, nodeValue, tagName, localName, prefix,
namespaceURI, name, localName, prefix, data, 

The return type is not stated for

insertBefore, replaceChild, removeChild, appendChild, normalize,
cloneNode, createElement, createElementNS, createTextNode,
createComment, createProcessingInstruction, createAttribute,
createAttributeNS, getElementsByTagName, getElementsByTagNameNS,

For many of these attributes and operations, the type seems obvious,
but since this is to replace the IDL, I think it should be stated.

Not mentioned is

getAttributeNode, setAttributeNode, ownerElement, 

Incorrectly mentioned is namespaceURI for Attr. 

Regards,
Martin