<?xml version="1.0" encoding="ISO-8859-1"?>
<?xml-stylesheet href="/stylesheets/webpage_html.xps" type="application/x-xpathscript"?>
<webpage>
<head>
<title>How AxKit Picks Stylesheets and/or Processors</title>
</head>
<body>
<section>
<title>Introduction</title>
<p>
AxKit works mainly by associating stylesheets (and by inference, a
stylesheet processor), with XML files when you request the XML file. The
process is defined in <a
href="http://www.w3.org/TR/REC-html40">REC-html40</a>, however the links
are confusing so I hope to clear things up a bit here.
</p>
<p>
Please note that while the specification we're talking about is the HTML
4 specification, this has nothing specifically to do with HTML. The <a
href="http://www.w3.org/TR/xml-stylesheet">xml-stylesheet</a> document
simply references the HTML 4 spec to save re-iterating what has already
been specified elsewhere.
</p>
</section>
<section>
<title>How it works</title>
<p>
When an XML file is encountered (determined by AxKit's XMLFinder module
- which checks first for a .xml extension, then for a <?xml?>
processing instruction), AxKit needs to determine how to process that
file. To do so it needs a list of stylesheets to process that file
against. The stylesheet type (a MIME type) determines the module used to
actually process the XML file together with the Stylesheet. It's also
worth noting that a stylesheet file isn't necessary if using a
DefaultStyleMap - this benefit could be useful, for example, for a
Cocoon-like XSP page where there is no stylesheet to interact with.
</p>
<p>
First, the <?xml-stylesheet?> processing instructions are considered
</p>
<p>
If the media doesn't match it is discarded immediately. Media types in
<?xml-stylesheet?> are processed as follows: First they are split
on /,\s*/. Then each element of the resulting array is stripped of
characters following and including the first non-ascii-alphanumeric
character. So "printer and dpi > 90" gets turned into "printer". Then they
are grepped for
/^screen|tty|printer|handheld|braille|tv|projection|aural|all$/ (case
sensitive). Finally the match test: A media type of "all" always matches
regardless of what is in preferred_media. Otherwise, a case sensitive
match is done (in perl terms, the "eq" operator). Provided a media
matches, then we go on to determine if this stylesheet should be used
depending on the title="..." attribute and the
alternate="..." attribute. The terms "Persistant", "Preferred" and
"Alternate" below are straight from REC-html40.
</p>
<subsection>
<title>Persistant Stylesheets</title>
<p>
If there is no title and alternate="no" (or no
alternate="..." attribute) then the stylesheet is added to the front of the list
of stylesheets - this is a persistant stylesheet and is _always_ applied
first (unless there are other persistant stylesheets, in which case this
is applied after those).
</p>
</subsection>
<subsection>
<title>Preferred Stylesheets</title>
<p>
If there is a title and alternate="no" (or no alternate attrib) then the
stylesheet is pushed onto the list of stylesheets to apply if there is
either no preferred_style, or preferred_style matches.
</p>
</subsection>
<subsection>
<title>Alternate Stylesheets</title>
<p>
If there is a title and alternate="yes", then the stylesheet is pushed
onto the list of stylesheets to apply if there is a preferred_style and it
matches the title.
</p>
</subsection>
<subsection>
<title>If all else fails</title>
<p>
Finally, just to be safe, StyleFinder maintains a list of
media="screen" stylesheets. If there are no stylesheets in the list at the
end of processing, the "screen" ones are used. Note though that the same
rules as above apply there too, and media="screen" is just used as a last
resort.
</p>
</subsection>
</section>
<section>
<title>And Finally...</title>
<p>
So when the parser that reads the <?xml-stylesheet?>'s returns, if it
returns a list of stylesheets, then fine. If not, we read
$cfg->DefaultStyleMap, the default implementation of which is to read the
AxAddDefaultStyleMap options in your httpd.conf or .htaccess. The details
of AxAddDefaultStyleMap are in the AxKit manpage.
</p>
</section>
</body>
</webpage>