Er... I meant "Yes, this is a problem where the HTML spec inherits
from SGML," not "Yes, this shows some problem with the SGML spec."
For example, you can experiment via the HTML validation service
to see which attribute values are case sensitive and which are not:
http://www.halsoft.com/html-val-svc/
1. <!-- select doctype above... -->
2. <HEAD>
3. <TITLE><!-- your title here --></TITLE>
4. </HEAD>
5. <BODY>
6. <!-- your HTML test data -->
7. <p><a rel=InSeNsItIvE href="sEnSiTiVe">
8. sdf</a>
9. </BODY>
10.
Parsed Output (Element Structure Information Set)
AVERSION CDATA -//IETF//DTD HTML//EN//2.0
(HTML
(HEAD
(TITLE
)TITLE
)HEAD
(BODY
-\n\n
(P
AHREF CDATA sEnSiTiVe
ANAME IMPLIED
AREL TOKEN INSENSITIVE
AREV IMPLIED
AURN IMPLIED
ATITLE IMPLIED
AMETHODS IMPLIED
(A
-\nsdf
)A
-\n
)P
)BODY
)HTML
C