I just noticed that RESP in elements like <SUPPLIED> is CDATA instead of
IDREF. Is there a rationale behind this? The Green Book (pp1171-2)
implies that it ought to be IDREF:
Value: must be one of the identifiers declared in the document header...
just like it does for the immediately following HAND (which _is_ IDREF).
This came to light while parsing a text when sgmls said there were no
errors but I knew there were RESPs with values that had no explanation
elsewhere (header or not).