These are convenience attributes. When there become too many of them, HTML
becomes a big, complex language and that's inconvenient. I would argue that
there are already too many of them, and that they continually confuse and
mislead people.
I don't think that there is an SGML-compatible way to specify an extension
interface for attributes. Otherwise we could take them out of the HTML
standard and treat them as a "standardized formatting extension." It would
at least be clear to people that they were _not_ like the other parts of HTML.
Paul Prescod
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Paul Prescod (mailto:papresco@calum.uwaterloo.ca)