The XHTML Family:
HTML in XML.

Steven Pemberton.

CWI, Amsterdam, and W3C.

Chair, W3C HTML and Forms Working Groups.

If we've got XML, do we need HTML?

This was a question asked at a two-day workshop in San Francisco.

The answer was "Yes":

People don't want to invent their own languages.
People are happy with a lingua franca.
Many processes are already geared to HTML.

Still need for improvement.

Move to XML.
Clean up.
Modularise.
Add new functionality.

The HTML Working group.

International membership, around 20 members.
Many major players (IBM, Microsoft, Netscape, Sun, etc).
Meets weekly by phone, quarterly face-to-face.
There was more to be worked out than we anticipated.
XHTML is the first major XML application, so all eyes are on us.
XML still has needed some wrinkles ironed out.
Much coordination with other groups.

Main aims of the XHTML family.

Transition to XML.
As generic XML as possible.
Clean up the language.
Return to structure, remove presentation elements.
Modularise.
Address wider needs: accessibility, international.
Remove need for much scripting.
New functionality: Forms, device-independent events.
Bring together diverging markups.

Plan of action.

HTML 4.01: corrected version.
XHTML 1.0: transitional version of HTML 4.01 in 3 flavours.
Modularisation: agreement on split and methodology.
XHTML Basic: Small devices.
Ruby: needed Asian markup.
XHTML 1.1: clean version of 1.0 strict + Ruby.
Events: accessible and device-independent.
Forms: more control.
Address accessibility.
XHTML 2.0: Putting it all together.

XHTML 1.0.

XHTML 1.0 is an XML-ised version of HTML 4.01.
Just like HTML 4.01, there are 3 versions: 'strict', 'transitional', and 'frameset'.
Designed to work on both 'legacy' and XML user agents.
Makes use of 'quirks' in existing HTML browsers.

Differences.

Because of the difference between SGML and XML, there are some necessary differences, for instance:

Use lower case: <p> not <P>.
Attributes are always quoted: <th colspan="2">.
Anchors use id attribute not name(and not just on <a> by the way):
<a id="index"> <p id="top">.

Use of a small number of guidelines allows XHTML to be served to HTML user agents as well as XML user agents.

Examples of Guidelines.

Use space before / of empty elements:
```
<br /> <hr /> <img src="foo.gif" />.
```
Don't use <hr></hr> form.
Use both name= and id= on <a>:
```
<a name= "index" id= "index"> ... </a>.
```
Beware: CSS has slightly different rules for HTML and XML.
Similarly, the DOM has differences for HTML and XML.

Example XHTML 1.0.

<!DOCTYPE html PUBLIC 
 "-//W3C//DTD XHTML 1.0 Strict//EN"
 "http://www.w3.org/TR/xhtml1/DTD/strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml"
      xml:lang="en">
  <head><title>Virtual Library</title></head>
  <body>
    <p>Moved to
       <a href="http://vlib.org/">vlib.org</a>.
    </p>
  </body>
</html>

Modularisation.

XHTML has been divided into a number of modules.
A module is a collection of elements and/or attributes that can be used as a building block to build a DTD or Schema (e.g.: tables, forms).
Some modules consist of a single element, or just add some attributes to existing elements.
Not all modules are independent: if you use some modules, they bring other modules with them, or change other modules.
A language can be built with just XHTML modules, or adding your own.

Use of Modularisation.

We originally defined Modularisation just for our own use, but it has turned out useful for other groups as well.
Future modules are planned (eg extended forms, new events).
Family members must use certain modules.
Other languages using modularisation as well (Math, SMIL, etc.)

XHTML Basic.

XHTML Basic is the first XHTML family-member to be defined using Modularisation.
It is designed for small devices, typically mobile telephones.
Already demonstrated on 3 handsets.
Soon a part of WAP 2.

XHTML 1.1.

XHTML 1.1 is the second family member to be defined using Modularisation.
Its main aim is to present a cleaned-up, non-transitional version of XHTML 1.0 strict (no frames).
It also adds Ruby markup.
Otherwise: no new functionality.

Ruby.

Example Ruby markup:

<ruby>
  <rb>WWW</rb>
  <rp>(</rp><rt>World Wide Web</rt><rp>)</rp>
</ruby>

Use CSS to describe presentation.

XHTML 2.0.

XHTML 2.0 is still in preparation.
New forms.
New events.
More accessibility.

Forms.

Being produced by a separate group.
Consists of three parts:
- data model,
- instances,
- user interface.
Will include much more client-side checking.
Form data will be sent to the server as XML.
Separates content from presentation (e.g. a radio button and a select box both allow you to select one from many, and you may want to use different choices on different devices).

Events.

Current events are almost all in terms of mouse: onclick, onmouseover, onfocus, etc.
Future event model will be device independent, and allow you to define your own new events.
Uses the DOM event model.

Accessibility problems.

A sighted person can work out the structure from the visual presentation.
A non-sighted person cannot: the structure must be present in the markup.
That is why new features were added to forms and tables in HTML 4, like <caption>.
Text would also benefit from such a treatment: not h1, h2 etc (which are subject to misuse) but nested sections with their own headings.

Example of structure.

<section>
    <h>XHTML</h>
    ...
    <section>
            <h>Structure</h>
            ...
    </section>
</section>

Conclusions.

XML with related technologies gives you the freedom to define and deliver your own document types.
HTML is still needed as a base-line markup.
The new HTML gives a transition path to the future.
New generation of XML+CSS browsers emerging.
Now: HTML4, XHTML 1.0, Modularisation, Basic, 1.1.
Very soon: Forms, Events, XHTML 2.0.

To Find Out More.

All XHTML developments are made public at www.w3.org/Markup.
Members of W3C can also look at www.w3.org/Markup/Group.
To get involved, join W3C!

The XHTML Family: HTML in XML.