SUB and SUP

Jukka Korpela (jkorpela@cc.hut.fi)
Wed, 30 Apr 1997 09:12:54 +0300 (EET DST)


Date: Wed, 30 Apr 1997 09:12:54 +0300 (EET DST)
From: Jukka Korpela <jkorpela@cc.hut.fi>
To: www-html@w3.org
Subject: SUB and SUP
Message-ID: <Pine.OSF.3.96.970430082715.21492C-100000@alpha.hut.fi>

I think the description of the elements SUB and SUP needs some
clarification. There seems to be so different interpretations
that the HTML language specification should make it clearer
which is the intended one.

HTML 3.2 spec classifies SUB and SUP as "font style elements". See
http://www.w3.org/pub/WWW/TR/REC-html32.html#font-style
It describes that "SUB places text in subscript style" and
"SUP places text in superscript style". This suggests that they are
to be intended as stylistic presentation only, not affecting the
_meaning_ of a text.

The internationalization RFC 2070 (to which I can't any reference on those
W3C pages which specifically discuss internationalization!), see e.g.
http://saturn.aichi-u.ac.jp/~mimasa/jweblint/rfc/rfc2070.html
for an HTML version, describes SUP and SUB as strictly stylistic: 
 "Many languages require superscript text for proper rendering: as an
 example, the French "Mlle Dupont" should have "lle" in superscript. The
 SUP element, and its sibling SUB for subscript text, are introduced to
 allow proper markup of such text. SUP and SUB contents are restricted to
 PCDATA to avoid nesting problems."

On the other hand, the ISO HTML proposal, see
http://www.ornl.gov/sgml/wg8/document/1901.htm
while still referring to SUB and SUP as "character style elements"
contains the example
  E = mc<SUP>2</SUP>
and such usage seems to be rather common in actual practise as well
as in various HTML tutorials.

When SUP is used for _exponents_, it has, of course, a definite
meaning instead of being just stylistic presentation. Usage like
M<SUP>lle</SUP> is clearly stylistic only, H<SUB>2</SUB>O or
x<SUB>1</SUB> (meaning a subscripted variable) might be regarded
as stylistic only although they might also be regarded as essential
to the contents of the message, but exponents are a different thing.
This should become evident if we take a slightly different but
very simple example: a<SUP>b</SUP>.

Thus, I think it should be make clear whether SUB and SUP are
intended to be used for stylistic presentation only, and if they
are, explicitly state that they should not be used for exponents in
mathematical expressions or in other contexts where it might change
the meaning of a piece of text if SUB and SUP elements were presented
as normal text.

Yucca, http://www.hut.fi/~jkorpela/