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XML Standards News;
HTML, XHTML, and CSS PR s Impact Web Pages
During the early fall, a number of Proposed
Recommendations have come out of W3C. These recommendations apply to HTML, which still
comprises the majority of data found on the Web today. Interestingly enough, the new PRs
strengthen HTML, yet in no way compromise the growing importance of XML
on the Web.
HTML 4.0 is a PR
The long awaited next generation of HTML is now a
Proposed Recommendation. But
what does this mean exactly?
With the emergence of XML, why would we need improvements to
HTML? Wasn t XML designed to
be the next generation HTML?
Well, it turns out that most agree that both HTML and
XML have a place on the Web.
HTML is still the foremost language for the encoding of Web
display. XML on the other
hand, is designed for the coding and interchange of structured data on
the Web. Never mind that we
can now view XML directly in Web browsers! HTML remains the preferred language for publishing
content on the Web.
So what s new about HTML 4.0? First there are some general
editorial changes to the HTML specification. These include the addition of style sheets for
the document based on W3C technical report styles, the addition of a
short table of contents, updates in the acknowledgments, and references
to the document character set are all ISO 10646, and one time to Unicode
to signal equivalence.
But some
technical changes/improvements have been made as well:
- Table
Cells: The definitions of rowspan and colspan
changed. Now spans are bounded by groups (rowgroups or
colgroups). Also when
"char=align" not supported by the user agent, behavior is
undefined.
- Anchor
Elements: It is legal for "name" and
"id" to appear in the same start tag when they are both
defined for an element. They must have identical values.
- Image
Elements: Addition of the name attribute for backwards
compatibility. A note that user agents must provide different
mechanisms for accessing the "longdesc" URI (of IMG) and
the "src" URI (of A) when an IMG is part of the content of
an A element was added.
- Image,
Object, and Applet Elements: The vspace
and hspace attribute definitions now look like the definitions of
other attributes. The
type of vspace, hspace, and border attribute values was changed from
"length" to "pixels".
- Form
Elements: Addition of the name attribute for backwards
compatibility.
- Client-side
Map Elements: The content model of the Map element
now allows authors to mix Area content and block-level
content.
- Attribute
Values: Section 3.2.2 states that attribute values may
now contain colons and underscores as well.
HTML Version 4.0 (subversion
4.01), specifies the text, multimedia, and hyperlink features of the
previous versions of HTML, HTML 4.01 supports more multimedia options,
scripting languages, style sheets, better printing facilities, and
documents that are more accessible to users with disabilities. HTML 4.01
also takes great strides towards the internationalization of documents
with the incorporation of UNICODE.
HTML 4.01 is an SGML application conforming to International
Standard ISO 8879 -- Standard Generalized Markup Language. An XML version of this Web
publishing tag set has also been developed. See XHTML!
XHTML Brings Two Worlds
Together
We have
HTML 4.0. And we have
XML! So what is XHTML? Is this something new? How does it differ from
HTML? Is XHTML really XML or
HTML??
XHTML 1.0 is a reformulation of HTML 4.0 as an
XML 1.0 application, and three DTDs
corresponding to the ones defined by HTML 4.0. The semantics of the
elements and their attributes are defined in the W3C Recommendation for
HTML 4.0. These semantics provide the foundation for future extensibility
of XHTML. Compatibility with existing HTML user agents is possible by
following a small set of guidelines.
So XHTML is both HTML and XML. It is in the simplest form an XML
version of HTML. This means
that XHTML is well formed HTML.
It has all the HTML 4.0 tags. But the rules of XML well-formedness apply. So XHTML tags must be correctly
nested. And XHTML tags must
have both start and end tags.
In HTML it is often acceptable to mark paragraph starts with the
<p> tag and not required the end tag. But in XHTML both the start and end paragraph tags
will be required. Also in
HTML we can use the same syntax for tags with content (such as paragraph
or headings) and tags that are empty, or have no content (such as
<br> or <img>).
But in XHTML, we need to use the special empty tag syntax to
indicate that these tags have no content and no ending tag. This means that <br> will
become <br/>.
Now we might ask, what is the sense of having an XML
version of the HTML tag set?
The answer can be twofold.
First, well-formed HTML can lead to lighter-weight browser/client
side software. This is a
definite advantage when browsing with new highly portable devices. Second, if our HTML is well
formed XML, we can follow the rules of XML to provide content
extensions. That is, XHTML
provides us with extensible HTML!
Paged Media Specifications in CSS3
A new Working Draft proposes an extension to CSS to permit finer
control over the paged presentation, both printed and online, of Web
pages. This proposal includes new properties for describing headers,
footers, footnotes and endnotes. In addition cross-references and
page-based counters, and page-dependent floating elements are described
in this document. It is
important to note that all these new CSS properties are for data
constructs usually found on the printed page, not on Web
pages. Clearly CSS is making
the transition to providing media independent presentation for HTML. With these paged media
extensions, HTML will not be just for the Web anymore. These features require other
features described here, such as cross-references and page-based
counters. In addition, page-dependent floating elements are described in
this proposed extension.
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