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Re: [xml-dev] Boolean attributes in XHTML/HTML5
- From: Peter Flynn <peter@silmaril.ie>
- To: xml-dev@lists.xml.org
- Date: Tue, 28 Feb 2012 22:05:52 +0000
On 10/02/12 14:18, David Carlisle wrote:
> On 10/02/2012 14:02, Len Bullard wrote:
>> Which doesn't answer the question why they didn't choose disabled="yes".
>
> I wasn't involved but presumably because that would lead people to think
> that the attribute value mattered and that disabled="no" meant something
> different from disabled="yes". The point about boolean attributes as
> interpreted by browsers is that they are true if they are there (with
> any value) and false if they are not there.
From memory, assisted by a trawl of the IETF HTML-WG at
https://listserv.heanet.ie/cgi-bin/wa?A0=HTML-WG, there was no decision
at all.
I believe the pre-HTML2 code samples (TBL?) originally used <option
selected> and <input type=radio checked> because it wasn't actually
meant to undergo a formal SGML validation, so the question of what
"checked" and "selected" implied (as attributes) was not under
consideration.
When we cast HTML2 as a DTD, the values had to be declared as
*something*, and creating an attribute called after the value you wanted
to minimise it to probably seemed like a good idea at the time. I don't
recall it ever being questioned.
> so in html you have <foo> and <foo disabled> as markup, in XML where you
> need to supply a value, disabled="disabled" is valid for legacy reasons,
> disabled="" is valid because that's what people thought the syntax was
> anyway and anything else including disabled="no" acts the same way as
> disabled="" but is classed as non conforming (which only matters to
> validators not to browsers)
There are lots of other attribute minimisations that could have been
used if formal validation had been on the cards. The following is valid
SGML, for example:
<!doctype html public "-//IETF//DTD HTML 2.0 Strict//EN">
<title>Test</title>
<form>
<ul>
<li><input radio>A
<li><input radio checked>B
<li><input radio>C
</ul>
<input submit>
</form>
But as most browser writers didn't actually know any SGML, the question
never arose.
///Peter
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