On the case-sensitive of XHTML/HTML [Was: Re: simple question]

Daniel Watson wrote:
> 
>         I was wondering if you could be kind enough to answer one simple
> question. Should HTML be upper or lower-cased. 

From XHTML 1.0 [1], section 4.2:

  "XHTML documents must use lower case for all HTML element 
   and attribute names. This difference is necessary because
   XML is case-sensitive e.g. <li> and <LI> are different tags."

[1] http://www.w3.org/TR/xhtml1/#diffs

For HTML 4.01:

About elements, from section 3.2.1 [2]:

  "Element names are always case-insensitive."

[2] http://www.w3.org/TR/html401/intro/sgmltut.html#h-3.2.1

About attribute names, from section 3.2.2 [3]:

    "Attribute names are always case-insensitive."

[3] http://www.w3.org/TR/html401/intro/sgmltut.html#h-3.2.2

About attribute values, from section 6.1 [4]:

   "Each attribute definition includes information about 
    the case-sensitivity of its values."

[4] http://www.w3.org/TR/html401/types.html#h-6.1

> I have books that say
> capitalize and I have books that say just the opposite. We are starting to
> implement XML now and we would like to start cleaning up our HTML for future
> browsers but I don't know which should be our standard, upper or lower.
> 
> If you could be so kind as to shed some light on this or point me to someone
> who could it would be greatly appreciated.
> 
> Thanks for your time,
> Daniel Watson
> TapeOnline.com

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Ian Jacobs (jacobs@w3.org)   http://www.w3.org/People/Jacobs
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