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Posted by Christian Hackl on December 18, 2007, 7:20 am
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Jukka K. Korpela schrieb:
> A schema validator, using suitable schema, can check much more than a
> DTD validator, for sure. However, this is about XML (including XHTML),
> and we can see from the lack of the magic "/" that the OP is using
> classic, nominally SGML based HTML.
No no, that's a misunderstanding. I thought the "img" issue was the
same, no matter whether HTML or XHTML was used. That's why I wrote
"(X)HTML". I just didn't want to make my posting unnecessarily long by
writing
<img src="img.png" alt="" width="100px" height="100px"> or <img
src="img.png" alt="" width="100px" height="100px" />
The question, in fact, arised in the context of XHTML :)
> Moreover, there is no normative schema for XHML 1.0. The schemas are
> just unofficial attempts at capturing the syntax requirements (partly
> formal, partly prose) in the XHTML 1.0 specification.
What about XHTML 1.1?
Are you telling me that there is no official (W3C) definition of what is
conforming XHTML 1.0?
In any case, I gained a lot of new insights from this thread, thank you all.
--
Christian Hackl
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Posted by Jukka K. Korpela on December 18, 2007, 12:50 pm
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Scripsit Christian Hackl:
>> Moreover, there is no normative schema for XHML 1.0. The schemas are
>> just unofficial attempts at capturing the syntax requirements (partly
>> formal, partly prose) in the XHTML 1.0 specification.
>
> What about XHTML 1.1?
The situation is the same. On the other hand, XHTML 1.1 is an exercise
in futility. Even if you fake it to be text/html (there's an eternal
debate over the issue whether this is even "legal"), it won't work in
current web browsers, in general - there are some nasty requirements in
XHTML 1.1 especially as regards to image maps. It's based on the
modularization idea, which is rather uninteresting as such, but its
authors could not help throwing in some real changes, mostly poorly
documented (like adding syntactic restrictions in the DTD without
bothering to mention them in the part that purports to document the
changes).
> Are you telling me that there is no official (W3C) definition of what
> is conforming XHTML 1.0?
No, I'm telling you that there is no normative _schema_. XHTML 1.0 is
defined in a quick and dirty way: the syntax is defined using a DTD (not
a schema), with some extra requirements written in prose, and with a
reference to HTML 4.01 as regards to any _meaning_ of the elements. This
leaves some issues open, so that there are different ways to write a
schema definition.
--
Jukka K. Korpela ("Yucca")
http://www.cs.tut.fi/~jkorpela/
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Posted by Christian Hackl on December 18, 2007, 2:34 pm
Please log in for more thread options Jukka K. Korpela ha scritto:
> Scripsit Christian Hackl:
>
>> Are you telling me that there is no official (W3C) definition of what
>> is conforming XHTML 1.0?
>
> No, I'm telling you that there is no normative _schema_. XHTML 1.0 is
> defined in a quick and dirty way: the syntax is defined using a DTD (not
> a schema), with some extra requirements written in prose, and with a
> reference to HTML 4.01 as regards to any _meaning_ of the elements. This
> leaves some issues open, so that there are different ways to write a
> schema definition.
OK, let's see if I got it...
There are some XHTML schemas published by the W3C, for example here:
http://www.w3.org/TR/xhtml1-schema/
However, those documents are just informal notes and are considered work
in progress, so they aren't exactly "official" schemas. Still, they are
good enough to be used by schema validators such as schneegans.de,
because they contain improvements such as concise formal definitions for
data types (which allows you, among other things, to formally define
that "width" and "height" must be integer values).
There is no official (normative) schema neither for XHTML 1.0 nor XHTML
1.1, there are just normative DTDs, which are unable to express
important requirements of the languages.
Is this correct?
--
Christian Hackl
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Posted by Jukka K. Korpela on December 18, 2007, 5:08 pm
Please log in for more thread options Scripsit Christian Hackl:
> OK, let's see if I got it...
I think you did.
> There are some XHTML schemas published by the W3C, for example here:
> http://www.w3.org/TR/xhtml1-schema/
>
> However, those documents are just informal notes and are considered
> work in progress, so they aren't exactly "official" schemas.
Right.
> Still,
> they are good enough to be used by schema validators such as
> schneegans.de, because they contain improvements such as concise
> formal definitions for data types
That's useful if you use XHTML and you know the rules, so that you can
check whether the error messages identify real problems. The schema
validator's output cannot be authoritative, since the schema isn't, but
it can still be useful.
> (which allows you, among other
> things, to formally define that "width" and "height" must be integer
> values).
Well, such a requirement _can_ be expressed in a DTD, assuming it means
restricting them to unsigned integers and you use an SGML-based DTD. For
example, the HTML 4.01 DTDs restrict the ROWS and COLS attributes of a
TEXTAREA element that way. The XHTML 1.0 DTDs don't, since XML DTDs are
less expressive and cannot specify such a requirement. On the other
hand, even in HTML 4.01 DTDs, the WIDTH and HEIGHT attributes are
essentially unrestricted, since SGML DTDs cannot express the requirement
"must be an unsigned integer or an unsigned integer followed by the '%'
sign".
> There is no official (normative) schema neither for XHTML 1.0 nor
> XHTML 1.1, there are just normative DTDs, which are unable to express
> important requirements of the languages.
>
> Is this correct?
Yes. I'd like to add that schemas, though more powerful, cannot
completely specify the languages, since they cannot express semantics
(meaning), and might have some limitations in the syntactic area as
well.
--
Jukka K. Korpela ("Yucca")
http://www.cs.tut.fi/~jkorpela/
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Posted by Christian Hackl on December 18, 2007, 6:50 pm
Please log in for more thread options Jukka K. Korpela scrisse:
> Scripsit Christian Hackl:
>
>> (which allows you, among other
>> things, to formally define that "width" and "height" must be integer
>> values).
>
> Well, such a requirement _can_ be expressed in a DTD, assuming it means
> restricting them to unsigned integers and you use an SGML-based DTD. [...]
> On the other hand, even in HTML 4.01 DTDs, the WIDTH and HEIGHT attributes
> are essentially unrestricted, since SGML DTDs cannot express the requirement
> "must be an unsigned integer or an unsigned integer followed by the '%'
> sign".
Oh, so the only reason the DTD does not restrict width/height to integer
values is that pesky possibility of specifiying percentages?
Interesting! It's always amazing for me to see how little I really know
about all that stuff.
Still, though, I wonder why the W3C would not just declare those
informative schemas authoritative and incorporate them into the official
validation service, but then again, what do I know about the wondrous
ways of the W3C? :)
--
Christian Hackl
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