| 1 | ==============
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| 2 | XHTML Degrader
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| 3 | ==============
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| 4 |
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| 5 | The XhtmlDegraderMiddleware class is designed to make it easier to deploy XHTML
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| 6 | contents onto the World Wide Web. The correct MIME media type for sending XHTML
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| 7 | is ``application/xhtml+xml`` -- the ``text/html`` media type is also acceptable
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| 8 | provided certain guidelines_ are followed.
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| 9 |
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| 10 | The vast majority of web browsers released from 2002 onwards have good XHTML
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| 11 | support; this includes the likes of Mozilla Firefox, Opera, and Apple Safari.
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| 12 | Notable exceptions include Lynx 2.8 and Internet Explorer 7. Such browsers
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| 13 | refuse to display XHTML, and present the user with a download dialog instead.
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| 14 |
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| 15 | The role of the XHTML Degrader, then, is to automatically detect when browsers
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| 16 | do not support XHTML, and to degrade the contents into something they're capable
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| 17 | of rendering instead.
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| 18 |
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| 19 | .. _guidelines: http://www.w3.org/TR/2002/REC-xhtml1-20020801/#guidelines
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| 20 |
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| 21 | Installation
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| 22 | ============
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| 23 |
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| 24 | Add the middleware
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| 25 | ``'django.contrib.xhtmldegrader.middleware.XhtmlDegraderMiddleware'`` to your
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| 26 | MIDDLEWARE_CLASSES_ setting. (If you use GZipMiddleware, you should ensure that
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| 27 | it appears in the list before XhtmlDegraderMiddleware, to allow the XHTML
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| 28 | Degrader to act first.)
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| 29 |
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| 30 | .. _MIDDLEWARE_CLASSES: ../settings/#middleware-classes
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| 31 |
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| 32 | How it works
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| 33 | ============
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| 34 |
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| 35 | XhtmlDegraderMiddleware checks the content type of all HTTP responses. If it's
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| 36 | set to the XHTML media type, the ``Accept`` header (and possibly ``User-Agent``
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| 37 | header) are examined to determine whether the requester can in fact handle
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| 38 | XHTML. If so, the contents is sent unaltered. If not, a number of silent
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| 39 | changes are made to make the response more friendly for XHTML-challenged
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| 40 | browsers and web crawlers.
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| 41 |
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| 42 | Firstly, the ``Content-Type`` header is set to the HTML media type. Any XML
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| 43 | processing instructions are removed, and a ``DOCTYPE`` is added if none is
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| 44 | present. In the case of Internet Explorer, this should ensure the content is
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| 45 | rendered in "standards compliance" mode. Empty elements are made to have a
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| 46 | space before their trailing slash, so for example ``<br/>`` becomes ``<br />``.
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| 47 |
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| 48 | If an HTTP response is already set to ``text/html``, or set to any media type
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| 49 | other than ``application/xhtml+xml``, the middleware will have no effect.
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| 50 |
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| 51 | Limitations
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| 52 | ===========
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| 53 |
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| 54 | The XHTML Degrader does not attempt to transform content into valid HTML 4.
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| 55 | This can be an advantage, however; for example, some XForms plug-ins for
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| 56 | Internet Explorer 7 expect to receive XHTML sent as ``text/html``.
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| 57 |
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| 58 | There are differences between how CSS, DOM and scripting work within HTML, and
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| 59 | how they behave within an XML document. One example is the case-sensitivity of
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| 60 | CSS selectors, another would be the usage of ``document.write``. Dealing with
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| 61 | any such issues is left to the developer.
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