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Applied leafstorm's html5faq patch

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Armin Ronacher 15 years ago
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  1. 1
      AUTHORS
  2. 191
      docs/htmlfaq.rst

1
AUTHORS
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@ -16,6 +16,7 @@ Patches and Suggestions
- Justin Quick
- Kenneth Reitz
- Marian Sigler
- Matthew Frazier
- Ron DuPlain
- Sebastien Estienne
- Simon Sapin

191
docs/htmlfaq.rst
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@ -2,66 +2,75 @@ HTML/XHTML FAQ
==============
The Flask documentation and example applications are using HTML5. You
will notice that in many situations when end tags are optional they are
not used to keep the HTML cleaner and also faster to load. Because there
is a lot of confusion about HTML and XHTML out there this document tries
to answer some of them.
may notice that in many situations, when end tags are optional they are
not used, so that the HTML is cleaner and faster to load. Because there
is much confusion about HTML and XHTML among developers, this document tries
to answer some of the major questions.
History on XHTML
History of XHTML
----------------
For a while it looked like HTML was about to be replaced by XHTML.
However barely any websites on the internet are actually real XHTML (which
means XHTML processed with XML rules). There are a couple of reasons why
this is the case. It mostly has to do with Internet Explorer which does
not accept the XHTML mimetype to switch the browser into XML mode.
However this is really easy to bypass but barely anyone does that. This
probably has to do with the fact that XHTML is really painful.
Why is it painful? XML has very strict errorhandling. On a parsing error
the browser is supposed to show the user an ugly error message. Most of
For a while, it appeared that HTML was about to be replaced by XHTML.
However, barely any websites on the Internet are actual XHTML (which is
HTML processed using XML rules). There are a couple of major reasons
why this is the case. One of them is Internet Explorer's lack of proper
XHTML support. The XHTML spec states that XHTML must be served with the MIME
type `application/xhtml+xml`, but Internet Explorer refuses to read files
with that MIME type.
While it is relatively easy to configure Web servers to serve XHTML properly,
few people do. This is likely because properly using XHTML can be quite
painful.
One of the most important causes of pain is XML's draconian (strict and
ruthless) error handling. When an XML parsing error is encountered,
the browser is supposed to show the user an ugly error message, instead
of attempting to recover from the error and display what it can. Most of
the (X)HTML generation on the web is based on non-XML template engines
(such as Jinja, the one used in Flask) which do not protect you from
accidentally creating invalid HTML. There are XML based template engines
but they usually come with a larger runtime overhead and are not as
straightforward to use because they have to obey XML rules.
Now the majority of users assumed they were using XHTML though. The
reasons for that is that they sticked an XHTML doctype on top of the
document and self-closed all necessary tags (``<br>`` becomes ``<br/>`` or
``<br></br>`` in XHTML). However even if the document properly validates
as XHTML there are still other things to keep in mind.
XHTML also changes the way you work with JavaScript because you now have
to use the namespaced DOM interface with the XHTML namespace to query for
HTML elements.
accidentally creating invalid XHTML. There are XML based template engines,
such as Kid and the popular Genshi, but they often come with a larger
runtime overhead and, are not as straightforward to use because they have
to obey XML rules.
The majority of users, however, assumed they were properly using XHTML.
They wrote an XHTML doctype at the top of the document and self-closed all
the necessary tags (``<br>`` becomes ``<br/>`` or ``<br></br>`` in XHTML).
However, even if the document properly validates as XHTML, what really
determines XHTML/HTML processing in browsers is the MIME type, which as
said before is often not set properly. So the valid XHTML was being treated
as invalid HTML.
XHTML also changed the way JavaScript is used. To properly work with XHTML,
programmers have to use the namespaced DOM interface with the XHTML
namespace to query for HTML elements.
History of HTML5
----------------
HTML5 was started in 2004 under the name Web Applications 1.0 by the
WHATWG (Apple, Mozilla, Opera) and the idea was to write a new and
improved specification of HTML based on actual browser behaviour instead
of behaviour that exists on the paper but could not be implemented
because of backwards compatibility with the already existing web.
Development of the HTML5 specification was started in 2004 under the name
"Web Applications 1.0" by the Web Hypertext Application Technology Working
Group, or WHATWG (which was formed by the major browser vendors Apple,
Mozilla, and Opera) with the goal of writing a new and improved HTML
specification, based on existing browser behaviour instead of unrealistic
and backwards-incompatible specifications.
For example in theory HTML4 ``<title/Hello/`` means exactly the same as
``<title>Hello</title>`` but because existing websites are using
pseudo-XHTML which uses the Slash in different ways, this could not be
implemented properly.
For example, in HTML4 ``<title/Hello/`` theoretically parses exactly the
same as ``<title>Hello</title>``. However, since people were using
XHTML-like tags along the lines of ``<link />``, browser vendors implemented
the XHTML syntax over the syntax defined by the specification.
In 2007 the specification was adopted as the basis of a new HTML
specification under the umbrella of the W3C. Currently it looks like
XHTML is losing traction, the XHTML 2 working group was disbanded and
HTML5 is being implemented by all major browser vendors.
In 2007, the specification was adopted as the basis of a new HTML
specification under the umbrella of the W3C, known as HTML5. Currently,
it appears that XHTML is losing traction, as the XHTML 2 working group has
een disbanded and HTML5 is being implemented by all major browser vendors.
HTML versus XHTML
-----------------
The following table gives you a quick overview of features available in
HTML 4.01, XHTML 1.1 and HTML5 (we are not looking at XHTML 1.0 here which
was superceeded by XHTML 1.1 or XHTML5 which is barely supported currently):
HTML 4.01, XHTML 1.1 and HTML5. (XHTML 1.0 is not included, as it was
superseded by XHTML 1.1 and the barely-used XHTML5.)
.. tabularcolumns:: |p{9cm}|p{2cm}|p{2cm}|p{2cm}|
@ -74,10 +83,10 @@ was superceeded by XHTML 1.1 or XHTML5 which is barely supported currently):
+-----------------------------------------+----------+----------+----------+
| ``<script/>`` supported | |N| | |Y| | |N| |
+-----------------------------------------+----------+----------+----------+
| might be served as `text/html` | |Y| | |N| [3]_ | |Y| |
| should be served as `text/html` | |Y| | |N| [3]_ | |Y| |
+-----------------------------------------+----------+----------+----------+
| might be served as | |N| | |Y| | |N| |
| `application/xml+html` | | | |
| should be served as | |N| | |Y| | |N| |
| `application/xhtml+xml` | | | |
+-----------------------------------------+----------+----------+----------+
| strict error handling | |N| | |Y| | |N| |
+-----------------------------------------+----------+----------+----------+
@ -89,12 +98,13 @@ was superceeded by XHTML 1.1 or XHTML5 which is barely supported currently):
+-----------------------------------------+----------+----------+----------+
| ``<audio>`` tag | |N| | |N| | |Y| |
+-----------------------------------------+----------+----------+----------+
| New semantical tags like ``<article>`` | |N| | |N| | |Y| |
| New semantic tags like ``<article>`` | |N| | |N| | |Y| |
+-----------------------------------------+----------+----------+----------+
.. [1] Obscure feature inherited from SGML not supported by browsers
.. [2] For compatibility with XHTML generating server code for some
tags such as ``<br>``. Should not be used.
.. [1] This is an obscure feature inherited from SGML. It is usually not
supported by browsers, for reasons detailed above.
.. [2] This is for compatibility with server code that generates XHTML for
tags such as ``<br>``. It should not be used in new code.
.. [3] XHTML 1.0 is the last XHTML standard that allows to be served
as `text/html` for backwards compatibility reasons.
@ -103,27 +113,30 @@ was superceeded by XHTML 1.1 or XHTML5 which is barely supported currently):
.. |N| image:: _static/no.png
:alt: No
What does Strict Mean?
----------------------
What does "strict" mean?
------------------------
HTML5 has strictly defined parsing rules, but it also specifies how a
browser should react to parsing errors. Some things people stumble upon
with HTML5 and older HTML standards is that browsers will accept some
things that still create the expected output even though it looks wrong
(eg: certain tags are missing or are not closed).
HTML5 has strictly defined parsing rules, but it also specifies exactly
how a browser should react to parsing errors - unlike XHTML, which simply
states parsing should abort. Some people are confused by apparently
invalid syntax that still generates the expected results (for example,
missing end tags or unquoted attribute values).
Some of that is caused by the error handling browsers use if they
encounter a markup error, others are actually specified. The following
things are optional in HTML5 by standard and have to be supported by
browsers (and are supported):
Some of these work because of the lenient error handling most browsers use
when they encounter a markup error, others are actually specified. The
following constructs are optional in HTML5 by standard, but have to be
supported by browsers:
- ``<html>``, ``<head>`` or ``<body>``
- The closing tags for ``<p>``, ``<li>``, ``<dl>``, ``<dd>``, ``<tr>``,
``<td>``, ``<th>``, ``<tbody>``, ``<thead>``, ``<tfoot>``.
- quotes for attribtues if they contain no whitespace and some
special chars that require quoting.
- Wrapping the document in an ``<html>`` tag
- Wrapping header elements in ``<head>`` or the body elements in
``<body>``
- Closing the ``<p>``, ``<li>``, ``<dl>``, ``<dd>``, ``<tr>``,
``<td>``, ``<th>``, ``<tbody>``, ``<thead>``, or ``<tfoot>`` tags.
- Quoting attributes, so long as they contain no whitespace or
special characters (like ``<``, ``>``, ``'``, or ``"``).
- Requiring boolean attributes to have a value.
This means the following piece of HTML5 is perfectly valid:
This means the following page in HTML5 is perfectly valid:
.. sourcecode:: html
@ -152,13 +165,43 @@ This means the following piece of HTML5 is perfectly valid:
</div>
New technologies in HTML5
-------------------------
HTML5 adds many new features that make Web applications easier to write
and to use.
- The ``<audio>`` and ``<video>`` tags provide a way to embed audio and
video without complicated add-ons like QuickTime and Flask.
- Semantic elements like ``<article>``, ``<header>``, ``<nav>``, and
``<time>`` that make content easier to understand.
- The ``<canvas>`` tag, which supports a powerful drawing API, reducing
the need for server-generated images to present data graphically.
- New form control types like ``<input type="date">`` that allow user
agents to make entering and validating values easier.
- Advanced JavaScript APIs like Web Storage, Web Workers, Web Sockets,
geolocation, and offline applications.
Many other features have been added, as well. A good guide to new features
in HTML5 is Mark Pilgrim's soon-to-be-published book, `Dive Into HTML5`_.
Not all of them are supported in browsers yet, however, so use caution.
_Dive into HTML5: http://www.diveintohtml5.org/
What should be used?
--------------------
Currently the answer is HTML5. There are very few reasons to use XHTML
with the latest development. There are some companies successfully using
actual XML and XSLT on the client side with fallbacks to server side HTML4
generation for browsers not supporting XML and XSLT but but it's not very
common. Now that MathML and SVG landed in HTML5 and with the sad support
for XHTML in Internet Explorer and many JavaScript libraries for most
applications no reasons remain to use XHTML.
Currently, the answer is HTML5. There are very few reasons to use XHTML
considering the latest developments in Web browsers. To summarize the
reasons given above:
- Internet Explorer (which, sadly, currently leads in market share)
has poor support for XHTML.
- Many JavaScript libraries also do not support XHTML, due to the more
complicated namespacing API it requires.
- HTML5 adds several new features, including semantic tags and the
long-awaited ``<audio>`` and ``<video>`` tags.
- It has the support of most browser vendors behind it.
- It is much easier to write, and more compact.
For most applications, it is undoubtably better to use HTML5 than XHTML.

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