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1.5 Standards and Extensions
The basic syntax and semantics of HTML
are defined in the HTML standard, now in its final version, 4.01.
HTML matured quickly, in barely a decade. At one time, a new version
would appear before you had a chance to finish reading an earlier
edition of this book. Today, HTML has stopped evolving. As far as the
W3C is concerned, XHTML has taken over. Now the wait is for browser
manufacturers to implement the standards.
The XHTML standard currently is
Version 1.0. Fortunately, XHTML Version 1.0 is, for the most part, a
reconstitution of HTML Version 4.0.1. There are some differences,
which we explore in Chapter 16. The popular
browsers continue to support HTML documents, so there is no cause to
stampede to XHTML. Do, however, start walking in that direction: a
newer XHTML version, 1.1, is under consideration at the W3C, and
browser developers are slowly but surely dropping nonstandard HTML
features from their products.
Obviously, browser developers rely upon
standards to have their software properly format and display common
HTML and XHTML documents. Authors use the standards to make sure they
are writing effective, correct documents that get displayed properly
by the browsers.
However, standards are not always explicit; manufacturers have some
leeway in how their browsers might display an element. And to
complicate matters, commercial forces have pushed developers to add
into their browsers nonstandard extensions meant to improve the
language.
Confused? Don't be: in this book, we explore in
detail the syntax, semantics, and idioms of the HTML Version 4.01 and
XHTML Version 1.0 languages, along with the many important extensions
that are supported in the latest versions of the most popular
browsers.
1.5.1 Nonstandard Extensions
It
doesn't take an advanced degree in The Obvious to
know that distinction draws attention. So, too, with browsers. Extra
whizbang features can give the edge in the otherwise standardized
browser market. That can be a nightmare for authors. A lot of people
want you to use the latest and greatest gimmick or even useful
HTML/XHTML extension. But it's not part of the
standard, and not all browsers support it. In fact, on occasion, the
popular browsers support different ways of doing the same thing.
1.5.2 Extensions: Pro and Con
Every software vendor adheres to the technological standards;
it's embarrassing to be incompatible, and your
competitors will take every opportunity to remind buyers of your
product's failure to comply, no matter how arcane or
useless that standard might be. At the same time, vendors seek to
make their products different from and better than the
competition's offerings. Netscape's
and Internet Explorer's extensions to standard HTML
are perfect examples of these market pressures.
Many document authors feel safe using these extended
browsers' nonstandard extensions because of their
combined and commanding share of users. For better or worse,
extensions to HTML in prominent browsers become part of the street
version of the language, much like English slang creeping into the
vocabulary of most Frenchmen, despite the best efforts of the
Académie Française.
Fortunately, with HTML Version 4.0, the W3C standards caught up with
the browser manufacturers. In fact, the tables turned somewhat. The
many extensions to HTML that originally appeared as extensions in
Netscape Navigator and Microsoft Internet Explorer are now part of
the HTML 4 and XHTML 1.0 standards, and there are other parts of the
new standard that are not yet features of the popular browsers.
1.5.3 Avoiding Extensions
In general, we
urge you to resist using extensions unless you have a compelling and
overriding reason to do so. By using them, particularly in key
portions of your documents, you run the risk of losing a substantial
portion of your potential readership. Sure, the Internet Explorer
community is large enough to make this point moot now, but even so,
you are excluding from your pages millions of people who use
Netscape.
Of course, there are varying degrees of dependency on extensions. If
you use some of the horizontal rule extensions, for example, most
other browsers will ignore the extended attributes and render a
conventional horizontal rule. On the other hand, reliance upon a
number of font-size changes and text-alignment extensions to control
your document's appearance will make your document
look terrible on many alternative browsers. It might not even display
at all on browsers that don't support the
extensions.
We admit that it is disingenuous of us to decry the use of extensions
while presenting complete descriptions of their use. In keeping with
the general philosophy of the Internet, we'll err on
the side of handing out rope and guns to all interested parties while
hoping you have enough smarts to keep from hanging yourself or
shooting yourself in the foot.
Our advice still holds, though: use an extension only where it is
necessary or very advantageous, and do so with the understanding that
you are disenfranchising a portion of your audience. To that end, you
might even consider providing separate, standards-based versions of
your documents to accommodate users of other browsers.
1.5.4 Extensions Through Modules
The upcoming
XHTML Version
1.1 provides a mechanism for extending the language in a standard
way: XML modules. In fact, XHTML 1.1 is comprised of modules itself.
XHTML modules divide the HTML language into discrete document types,
each defining features and functions that are parts of the language.
There are separate modules for XHTML forms, text, scripting, tables,
and so on all the nondeprecated elements of XHTML 1.0.
The advantage of modules is extensibility. In addition to using the
markup features from the XHTML modules normally included in the
standard, the new language lets you easily blend other XML modules
into your documents, extending their features and capabilities in a
standard way. For instance, the W3C has defined a MathML module that
provides explicit markup elements for mathematical equations that you
could use in your next XHTML-based math thesis.
Modules, let alone the XHTML Version 1.1 language, are experimental
and are not well supported by the popular browsers. Accordingly, we
don't recommend that you use XHTML modules just yet.
For now, the subject is beyond the scope of this book. Consult the
W3C web site for more details.
