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Added news about the release of 1.0.19, Daniel
This commit is contained in:
Daniel Veillard
@@ -78,22 +78,22 @@ A:link, A:visited, A:active { text-decoration: underline }
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<h3>Table of contents</h3>
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<ul>
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<li><a href="internals.html#Introducti">Introduction</a></li>
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<li><a href="internals.html#Basics">Basics</a></li>
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<li><a href="internals.html#Keep">Keep it simple stupid</a></li>
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<li><a href="internals.html#libxml">The libxml nodes</a></li>
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<li><a href="internals.html#XSLT">The XSLT processing steps</a></li>
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<li><a href="internals.html#XSLT1">The XSLT stylesheet compilation</a></li>
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<li><a href="internals.html#XSLT2">The XSLT template compilation</a></li>
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<li><a href="internals.html#processing">The processing itself</a></li>
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<li><a href="internals.html#XPath">XPath expressions compilation</a></li>
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<li><a href="internals.html#XPath1">XPath interpretation</a></li>
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<li><a href="internals.html#Descriptio">Description of XPath
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<li><a href="internals.html#Basics">Basics</a></li>
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<li><a href="internals.html#Keep">Keep it simple stupid</a></li>
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<li><a href="internals.html#libxml">The libxml nodes</a></li>
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<li><a href="internals.html#XSLT">The XSLT processing steps</a></li>
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<li><a href="internals.html#XSLT1">The XSLT stylesheet compilation</a></li>
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<li><a href="internals.html#XSLT2">The XSLT template compilation</a></li>
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<li><a href="internals.html#processing">The processing itself</a></li>
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<li><a href="internals.html#XPath">XPath expressions compilation</a></li>
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<li><a href="internals.html#XPath1">XPath interpretation</a></li>
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<li><a href="internals.html#Descriptio">Description of XPath
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Objects</a></li>
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<li><a href="internals.html#XPath3">XPath functions</a></li>
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<li><a href="internals.html#stack">The variables stack frame</a></li>
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<li><a href="internals.html#Extension">Extension support</a></li>
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<li><a href="internals.html#Futher">Further reading</a></li>
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<li><a href="internals.html#TODOs">TODOs</a></li>
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<li><a href="internals.html#XPath3">XPath functions</a></li>
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<li><a href="internals.html#stack">The variables stack frame</a></li>
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<li><a href="internals.html#Extension">Extension support</a></li>
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<li><a href="internals.html#Futher">Further reading</a></li>
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<li><a href="internals.html#TODOs">TODOs</a></li>
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</ul>
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<h3><a name="Introducti2">Introduction</a></h3>
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<p>This document describes the processing of <a href="http://xmlsoft.org/XSLT/">libxslt</a>, the <a href="http://www.w3.org/TR/xslt">XSLT</a> C library developed for the <a href="http://www.gnome.org/">Gnome</a> project.</p>
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@@ -107,10 +107,10 @@ stylesheet document and generates an output document:</p>
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the following operations:</p>
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<ul>
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<li>parsing files</li>
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<li>building the in-memory DOM structure associated with the documents
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<li>building the in-memory DOM structure associated with the documents
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handled</li>
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<li>the XPath implementation</li>
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<li>serializing back the result document to XML and HTML. (Text is handled
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<li>the XPath implementation</li>
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<li>serializing back the result document to XML and HTML. (Text is handled
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directly.)</li>
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</ul>
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<h3><a name="Keep1">Keep it simple stupid</a></h3>
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@@ -129,7 +129,7 @@ stylesheets. In general the implementation of libxslt follows the following
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pattern:</p>
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<ul>
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<li>KISS (keep it simple stupid)</li>
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<li>when there is a clear bottleneck optimize on top of this simple
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<li>when there is a clear bottleneck optimize on top of this simple
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framework and refine only as much as is needed to reach the expected
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result</li>
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</ul>
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@@ -148,19 +148,19 @@ variations depending on the node type:</p>
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indicates the kind of node it represents, the most common ones are:</p>
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<ul>
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<li>document nodes</li>
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<li>element nodes</li>
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<li>text nodes</li>
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<li>element nodes</li>
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<li>text nodes</li>
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</ul>
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<p>For the XSLT processing, entity nodes should not be generated (i.e. they
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should be replaced by their content). Most nodes also contains the following
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"navigation" informations:</p>
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<ul>
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<li>the containing <strong>doc</strong>ument</li>
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<li>the <strong>parent</strong> node</li>
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<li>the first <strong>children</strong> node</li>
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<li>the <strong>last</strong> children node</li>
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<li>the <strong>prev</strong>ious sibling</li>
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<li>the following sibling (<strong>next</strong>)</li>
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<li>the <strong>parent</strong> node</li>
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<li>the first <strong>children</strong> node</li>
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<li>the <strong>last</strong> children node</li>
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<li>the <strong>prev</strong>ious sibling</li>
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<li>the following sibling (<strong>next</strong>)</li>
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</ul>
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<p>Elements nodes carries the list of attributes in the properties, an
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attribute itself holds the navigation pointers and the children list (the
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@@ -176,21 +176,21 @@ used by the application to hold specific data on this node.</p>
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level:</p>
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<ol>
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<li>parse the stylesheet and generate a DOM tree</li>
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<li>take the stylesheet tree and build a compiled version of it (the
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<li>take the stylesheet tree and build a compiled version of it (the
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compilation phase)</li>
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<li>take the input and generate a DOM tree</li>
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<li>process the stylesheet against the input tree and generate an output
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<li>take the input and generate a DOM tree</li>
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<li>process the stylesheet against the input tree and generate an output
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tree</li>
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<li>serialize the output tree</li>
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<li>serialize the output tree</li>
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</ol>
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<p>A few things should be noted here:</p>
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<ul>
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<li>the steps 1/ 3/ and 5/ are optional</li>
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<li>the stylesheet obtained at 2/ can be reused by multiple processing 4/
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<li>the stylesheet obtained at 2/ can be reused by multiple processing 4/
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(and this should also work in threaded programs)</li>
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<li>the tree provided in 2/ should never be freed using xmlFreeDoc, but by
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<li>the tree provided in 2/ should never be freed using xmlFreeDoc, but by
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freeing the stylesheet.</li>
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<li>the input tree 4/ is not modified except the _private field which may
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<li>the input tree 4/ is not modified except the _private field which may
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be used for labelling keys if used by the stylesheet</li>
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</ul>
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<h3><a name="XSLT1">The XSLT stylesheet compilation</a></h3>
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@@ -267,22 +267,22 @@ applying the following algorithm:</p>
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hash table, walking the hash list until the node satisfies all the steps
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of the pattern, then checking the appropriate(s) global templates to see
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if there isn't a higher priority rule to apply</li>
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<li>If there is no template, apply the default rule (recurse on the
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<li>If there is no template, apply the default rule (recurse on the
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children)</li>
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<li>else walk the content list of the selected templates, for each of them:
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<li>else walk the content list of the selected templates, for each of them:
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<ul>
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<li>if the node is in the XSLT namespace then the node has a _private
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field pointing to the preprocessed values, jump to the specific
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code</li>
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<li>if the node is in an extension namespace, look up the associated
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<li>if the node is in an extension namespace, look up the associated
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behavior</li>
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<li>otherwise copy the node.</li>
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</ul>
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<li>otherwise copy the node.</li>
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</ul>
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<p>The closure is usually done through the XSLT
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<strong>apply-templates</strong> construct recursing by applying the
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adequate template on the input node children or on the result of an
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associated XPath selection lookup.</p>
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</li>
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</li>
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</ol>
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<p>Note that large parts of the input tree may not be processed by a given
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stylesheet and that on the opposite some may be processed multiple times.
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@@ -292,15 +292,15 @@ logic. <strong>xsltApplyStylesheet()</strong> is the entry point, it
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allocates an xsltTransformContext containing the following:</p>
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<ul>
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<li>a pointer to the stylesheet being processed</li>
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<li>a stack of templates</li>
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<li>a stack of variables and parameters</li>
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<li>an XPath context</li>
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<li>the template mode</li>
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<li>current document</li>
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<li>current input node</li>
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<li>current selected node list</li>
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<li>the current insertion points in the output document</li>
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<li>a couple of hash tables for extension elements and functions</li>
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<li>a stack of templates</li>
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<li>a stack of variables and parameters</li>
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<li>an XPath context</li>
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<li>the template mode</li>
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<li>current document</li>
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<li>current input node</li>
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<li>current selected node list</li>
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<li>the current insertion points in the output document</li>
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<li>a couple of hash tables for extension elements and functions</li>
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</ul>
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<p>Then a new document gets allocated (HTML or XML depending on the type of
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output), the user parameters and global variables and parameters are
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@@ -335,7 +335,7 @@ containing the parsed expression tree, for example the expression:</p>
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<p>This can be tested using the <code>testXPath</code> command (in the
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libxml codebase) using the <code>--tree</code> option.</p>
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<p>Again, the KISS approach is used. No optimization is done. This could be
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an interesting thing to add. <a href="http://www-106.ibm.com/developerworks/library/x-xslt2/?dwzone=x?open&l=132%2ct=gr%2c%2Bp=saxon">Michael
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an interesting thing to add. <a href="http://www-106.ibm.com/developerworks/library/x-xslt2/?dwzone=x?open&l=132%2ct=gr%2c+p=saxon">Michael
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Kay describes</a> a lot of possible and interesting optimizations done in
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Saxon which would be possible at this level. I'm unsure they would provide
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much gain since the expressions tends to be relatively simple in general and
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@@ -354,13 +354,13 @@ transformation the context is maintained within the XSLT context. Its content
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follows the requirements from the XPath specification:</p>
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<ul>
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<li>the current document</li>
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<li>the current node</li>
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<li>a hash table of defined variables (but not used by XSLT)</li>
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<li>a hash table of defined functions</li>
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<li>the proximity position (the place of the node in the current node
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<li>the current node</li>
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<li>a hash table of defined variables (but not used by XSLT)</li>
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<li>a hash table of defined functions</li>
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<li>the proximity position (the place of the node in the current node
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list)</li>
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<li>the context size (the size of the current node list)</li>
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<li>the array of namespace declarations in scope (there also is a namespace
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<li>the context size (the size of the current node list)</li>
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<li>the array of namespace declarations in scope (there also is a namespace
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hash table but it is not used in the XSLT transformation).</li>
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</ul>
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<p>For the purpose of XSLT an <strong>extra</strong> pointer has been added
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@@ -403,17 +403,17 @@ the stack).</p>
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<ul>
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<li>check <code>nargs</code> for proper handling of errors or functions
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with variable numbers of parameters</li>
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<li>pop the parameters from the stack using <code>obj =
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<li>pop the parameters from the stack using <code>obj =
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valuePop(ctxt);</code>
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</li>
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<li>do the function specific computation</li>
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<li>push the result parameter on the stack using <code>valuePush(ctxt,
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<li>do the function specific computation</li>
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<li>push the result parameter on the stack using <code>valuePush(ctxt,
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res);</code>
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</li>
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<li>free up the input parameters with
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<li>free up the input parameters with
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<code>xmlXPathFreeObject(obj);</code>
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</li>
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<li>return</li>
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<li>return</li>
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</ul>
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<p>Sometime the work can be done directly by modifying in-situ the top object
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on the stack <code>ctxt->value</code>.</p>
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@@ -435,7 +435,7 @@ the code will be stable. <span style="background-color: #FF0000">TODO</span>
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<p>There is a separate document explaining <a href="extensions.html">how the
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extension support works</a>.</p>
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<h3><a name="Futher">Further reading</a></h3>
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<p>Michael Kay wrote <a href="http://www-106.ibm.com/developerworks/library/x-xslt2/?dwzone=x?open&l=132%2ct=gr%2c%2Bp=saxon">a
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<p>Michael Kay wrote <a href="http://www-106.ibm.com/developerworks/library/x-xslt2/?dwzone=x?open&l=132%2ct=gr%2c+p=saxon">a
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really interesting article on Saxon internals</a> and the work he did on
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performance issues. I wishes I had read it before starting libxslt design (I
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would probably have avoided a few mistakes and progressed faster). A lot of
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@@ -452,11 +452,11 @@ for output should be added directly to libxml).</p>
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especially:</p>
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<ul>
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<li>static slot allocation on the stack frame</li>
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<li>specific boolean interpretation of an XPath expression</li>
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<li>some of the sorting optimization</li>
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<li>Lazy evaluation of location path. (this may require more changes but
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<li>specific boolean interpretation of an XPath expression</li>
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<li>some of the sorting optimization</li>
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<li>Lazy evaluation of location path. (this may require more changes but
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sounds really interesting. XT does this too.)</li>
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<li>Optimization of an expression tree (This could be done as a completely
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<li>Optimization of an expression tree (This could be done as a completely
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independent module.)</li>
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</ul>
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<p>
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