opml:
attributes to be added to the XML spec itself, which struck me as equal parts widhful thinking and slippery slope. What he really wanted was for people to either explcitly include, or provide people with the option to add via parameter entities something along the lines of...
<!ENTITY % opmlText "CDATA #REQUIRED"> <!ENTITY % opmlLink "CDATA #REQUIRED"> ... <!ELEMENT foo (yadda,yadda,yadda)> <!ATTLIST foo %opmlText;>...which then lets him massage any XML document into OPML and vice versa. Parameter entities, or whatever the suitably nightmarish namespace equivalent is for xsd are, allow people to say "yes, and..." and provide context for tools to validate and try and do the right thing. So long as you're okay that the various tools may play fast and easy with your more esoteric changes, everyone is happy. So, while I'm not quite ready to jump on the REST bandwagon, when I look at everything I've just said in combination with clever hacks like this browser-based xml content editor I start to wonder. But I digress...