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<?xml version="1.0" standalone="no"?>
<!DOCTYPE s1 SYSTEM "../../style/dtd/document.dtd">
<!--
* Copyright 2001-2004 The Apache Software Foundation.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
-->
<!-- $Id: xsl_include_design.xml 337884 2004-02-17 19:29:35Z minchau $ -->
<s1 title="<xsl:include> / <xsl:import>">
<s2 title="Contents">
<ul>
<li><link anchor="functionality">Functionality</link></li>
<li><link anchor="implementation">Implementation</link></li>
</ul>
</s2>
<anchor name="functionality"/>
<s2 title="Functionality">
<p><code><xsl:include></code> allows you to include one stylesheet
into another. The includ<em>ed</em> stylesheet's templates will have the same
default priorities and import precedence as the includ<em>ing</em> stylesheet.
<code><xsl:import></code> offers the same, but the import precedence
of elements in an import<em>ed</em> stylesheet is always less than that of
the import<em>ing</em> stylesheet.</p>
</s2>
<anchor name="implementation"/>
<s2 title="Implementation">
<anchor name="include"/>
<s3 title="<xsl:include>">
<p>This is the simplest case, so we will look at that first. The algorithm
for including another stylesheet is roughly:</p>
<ul>
<li>get the including stylesheet from the XSLT parser</li>
<li>get the value of the "href" attribute from the
<code><xsl:include></code> element and check for circular
includes/imports</li>
<li>check if there is a defined <code>SourceLoader</code> set either
through the native or the TrAX API</li>
<li>get an <code>InputSource</code> for the document to include, either
from the <code>SourceLoader</code> or from the document's URI</li>
<li>parse the input document using the compiler's XSLT parser</li>
<li>set the import precedence of the included stylesheet to the same as
the import precedence of the including stylesheet</li>
<li>get the top-level stylesheet from the XSLT parser</li>
<li>move all variables, parameters, and top-level elements (include
templates) from the included stylesheet to the top-level stylesheet
(all elements will keep their import precedence even after being moved
to the top-level stylesheet)</li>
</ul>
</s3>
<anchor name="import"/>
<s3 title="<xsl:import>">
<p>This is very similar to <code><xsl:include></code>, but import
precedence has to be handled differently. Looking at the code you'll find
this fragment:</p><source>
// Handle precedence for the including stylesheet
final int currPrecedence = parser.getCurrentImportPrecedence();
final int nextPrecedence = parser.getNextImportPrecedence();
_imported.setImportPrecedence(currPrecedence);
context.setImportPrecedence(nextPrecedence);</source>
<p>The important thing here is that the imported stylesheet has import
precedence <em>less</em> than the importing stylesheet. So the imported
stylesheet gets the current import precedence, while the current stylesheet
gets the next available (unused) import precedence. The
<code>Stylesheet</code> class has a method
<code>setImportPrecedence()</code> that ensures that the import precedence
is set not only for the stylesheet itself, but that it is also propagated
down to any included/imported stylesheets:</p><source>
public void setImportPrecedence(final int precedence) {
// Set import precedence for this stylesheet
_importPrecedence = precedence;
// Set import precedence for all included stylesheets
final Enumeration elements = elements();
while (elements.hasMoreElements()) {
SyntaxTreeNode child = (SyntaxTreeNode)elements.nextElement();
if (child instanceof Include) {
Stylesheet included = ((Include)child).getIncludedStylesheet();
if (included != null) included.setImportPrecedence(precedence);
}
}
// Set import precedence for the stylesheet that imported this one
if (_importedFrom != null) {
if (_importedFrom.getImportPrecedence() < precedence) {
final Parser parser = getParser();
final int nextPrecedence = parser.getNextImportPrecedence();
_importedFrom.setImportPrecedence(nextPrecedence);
}
}
// Set import precedence for the stylesheet that included this one
else if (_includedFrom != null) {
if (_includedFrom.getImportPrecedence() != precedence)
_includedFrom.setImportPrecedence(precedence);
}
}</source>
<p>This method has been carefully cluttered together, and it works, and it
should not be touched.</p>
</s3>
<anchor name="apply-imports"/>
<s3 title="<xsl:apply-imports>">
</s3>
</s2>
</s1>
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