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diff --git a/app/static/doc/flask-docs/_sources/htmlfaq.txt b/app/static/doc/flask-docs/_sources/htmlfaq.txt new file mode 100644 index 0000000..1da25f3 --- /dev/null +++ b/app/static/doc/flask-docs/_sources/htmlfaq.txt @@ -0,0 +1,207 @@ +HTML/XHTML FAQ +============== + +The Flask documentation and example applications are using HTML5. You +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 of XHTML +---------------- + +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 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 +---------------- + +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 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, known as HTML5. Currently, +it appears that XHTML is losing traction, as the XHTML 2 working group has +been 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. (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}| + ++-----------------------------------------+----------+----------+----------+ +| | HTML4.01 | XHTML1.1 | HTML5 | ++=========================================+==========+==========+==========+ +| ``<tag/value/`` == ``<tag>value</tag>`` | |Y| [1]_ | |N| | |N| | ++-----------------------------------------+----------+----------+----------+ +| ``<br/>`` supported | |N| | |Y| | |Y| [2]_ | ++-----------------------------------------+----------+----------+----------+ +| ``<script/>`` supported | |N| | |Y| | |N| | ++-----------------------------------------+----------+----------+----------+ +| should be served as `text/html` | |Y| | |N| [3]_ | |Y| | ++-----------------------------------------+----------+----------+----------+ +| should be served as | |N| | |Y| | |N| | +| `application/xhtml+xml` | | | | ++-----------------------------------------+----------+----------+----------+ +| strict error handling | |N| | |Y| | |N| | ++-----------------------------------------+----------+----------+----------+ +| inline SVG | |N| | |Y| | |Y| | ++-----------------------------------------+----------+----------+----------+ +| inline MathML | |N| | |Y| | |Y| | ++-----------------------------------------+----------+----------+----------+ +| ``<video>`` tag | |N| | |N| | |Y| | ++-----------------------------------------+----------+----------+----------+ +| ``<audio>`` tag | |N| | |N| | |Y| | ++-----------------------------------------+----------+----------+----------+ +| New semantic tags like ``<article>`` | |N| | |N| | |Y| | ++-----------------------------------------+----------+----------+----------+ + +.. [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. + +.. |Y| image:: _static/yes.png + :alt: Yes +.. |N| image:: _static/no.png + :alt: No + +What does "strict" mean? +------------------------ + +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 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: + +- Wrapping the document in an ``<html>`` tag +- Wrapping header elements in ``<head>`` or the body elements in + ``<body>`` +- Closing the ``<p>``, ``<li>``, ``<dt>``, ``<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 page in HTML5 is perfectly valid: + +.. sourcecode:: html + + <!doctype html> + <title>Hello HTML5</title> + <div class=header> + <h1>Hello HTML5</h1> + <p class=tagline>HTML5 is awesome + </div> + <ul class=nav> + <li><a href=/index>Index</a> + <li><a href=/downloads>Downloads</a> + <li><a href=/about>About</a> + </ul> + <div class=body> + <h2>HTML5 is probably the future</h2> + <p> + There might be some other things around but in terms of + browser vendor support, HTML5 is hard to beat. + <dl> + <dt>Key 1 + <dd>Value 1 + <dt>Key 2 + <dd>Value 2 + </dl> + </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 or Flash. +- 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 +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 undoubtedly better to use HTML5 than XHTML. |