216 lines
9.2 KiB
HTML
216 lines
9.2 KiB
HTML
<!DOCTYPE html>
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<!-- This manual documents Guile version 3.0.10.
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Copyright (C) 1996-1997, 2000-2005, 2009-2023 Free Software Foundation,
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Inc.
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Copyright (C) 2021 Maxime Devos
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Copyright (C) 2024 Tomas Volf
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Permission is granted to copy, distribute and/or modify this document
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any later version published by the Free Software Foundation; with no
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Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A
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copy of the license is included in the section entitled "GNU Free
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Documentation License." -->
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<title>SXML Tree Fold (Guile Reference Manual)</title>
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<meta name="description" content="SXML Tree Fold (Guile Reference Manual)">
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<meta name="keywords" content="SXML Tree Fold (Guile Reference Manual)">
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<link href="index.html" rel="start" title="Top">
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<link href="Concept-Index.html" rel="index" title="Concept Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="SXML.html" rel="up" title="SXML">
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<link href="SXPath.html" rel="next" title="SXPath">
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<link href="Transforming-SXML.html" rel="prev" title="Transforming SXML">
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<body lang="en">
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<div class="subsection-level-extent" id="SXML-Tree-Fold">
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<div class="nav-panel">
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<p>
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Next: <a href="SXPath.html" accesskey="n" rel="next">SXPath</a>, Previous: <a href="Transforming-SXML.html" accesskey="p" rel="prev">Transforming SXML</a>, Up: <a href="SXML.html" accesskey="u" rel="up">SXML</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<h4 class="subsection" id="SXML-Tree-Fold-1"><span>7.21.5 SXML Tree Fold<a class="copiable-link" href="#SXML-Tree-Fold-1"> ¶</a></span></h4>
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<ul class="mini-toc">
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<li><a href="#Overview-1" accesskey="1">Overview</a></li>
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<li><a href="#Usage-2" accesskey="2">Usage</a></li>
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</ul>
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<div class="subsubsection-level-extent" id="Overview-1">
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<h4 class="subsubsection"><span>7.21.5.1 Overview<a class="copiable-link" href="#Overview-1"> ¶</a></span></h4>
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<p><code class="code">(sxml fold)</code> defines a number of variants of the <em class="dfn">fold</em>
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algorithm for use in transforming SXML trees. Additionally it defines
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the layout operator, <code class="code">fold-layout</code>, which might be described as a
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context-passing variant of SSAX’s <code class="code">pre-post-order</code>.
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</p>
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</div>
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<div class="subsubsection-level-extent" id="Usage-2">
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<h4 class="subsubsection"><span>7.21.5.2 Usage<a class="copiable-link" href="#Usage-2"> ¶</a></span></h4>
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<dl class="first-deffn">
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<dt class="deffn" id="index-foldt"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">foldt</strong> <var class="def-var-arguments">fup fhere tree</var><a class="copiable-link" href="#index-foldt"> ¶</a></span></dt>
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<dd><p>The standard multithreaded tree fold.
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</p>
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<p><var class="var">fup</var> is of type [a] -> a. <var class="var">fhere</var> is of type object -> a.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-foldts-1"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">foldts</strong> <var class="def-var-arguments">fdown fup fhere seed tree</var><a class="copiable-link" href="#index-foldts-1"> ¶</a></span></dt>
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<dd><p>The single-threaded tree fold originally defined in SSAX. See <a class="xref" href="SSAX.html">SSAX: A Functional XML Parsing Toolkit</a>,
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for more information.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-foldts_002a"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">foldts*</strong> <var class="def-var-arguments">fdown fup fhere seed tree</var><a class="copiable-link" href="#index-foldts_002a"> ¶</a></span></dt>
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<dd><p>A variant of <code class="code">foldts</code> that allows pre-order tree
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rewrites. Originally defined in Andy Wingo’s 2007 paper,
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<em class="emph">Applications of fold to XML transformation</em>.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-fold_002dvalues"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">fold-values</strong> <var class="def-var-arguments">proc list . seeds</var><a class="copiable-link" href="#index-fold_002dvalues"> ¶</a></span></dt>
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<dd><p>A variant of <code class="code">fold</code> that allows multi-valued seeds. Note that the
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order of the arguments differs from that of <code class="code">fold</code>. See <a class="xref" href="SRFI_002d1-Fold-and-Map.html">Fold, Unfold & Map</a>.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-foldts_002a_002dvalues"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">foldts*-values</strong> <var class="def-var-arguments">fdown fup fhere tree . seeds</var><a class="copiable-link" href="#index-foldts_002a_002dvalues"> ¶</a></span></dt>
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<dd><p>A variant of <code class="code">foldts*</code> that allows multi-valued
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seeds. Originally defined in Andy Wingo’s 2007 paper, <em class="emph">Applications
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of fold to XML transformation</em>.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-fold_002dlayout"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">fold-layout</strong> <var class="def-var-arguments">tree bindings params layout stylesheet</var><a class="copiable-link" href="#index-fold_002dlayout"> ¶</a></span></dt>
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<dd><p>A traversal combinator in the spirit of <code class="code">pre-post-order</code>.
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See <a class="xref" href="Transforming-SXML.html">Transforming SXML</a>.
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</p>
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<p><code class="code">fold-layout</code> was originally presented in Andy Wingo’s 2007 paper,
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<em class="emph">Applications of fold to XML transformation</em>.
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</p>
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<div class="example">
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<pre class="example-preformatted">bindings := (<binding>...)
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binding := (<tag> <handler-pair>...)
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| (*default* . <post-handler>)
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| (*text* . <text-handler>)
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tag := <symbol>
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handler-pair := (pre-layout . <pre-layout-handler>)
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| (post . <post-handler>)
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| (bindings . <bindings>)
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| (pre . <pre-handler>)
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| (macro . <macro-handler>)
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</pre></div>
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<dl class="table">
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<dt><var class="var">pre-layout-handler</var></dt>
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<dd><p>A function of three arguments:
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</p>
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<dl class="table">
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<dt><var class="var">kids</var></dt>
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<dd><p>the kids of the current node, before traversal
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</p>
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</dd>
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<dt><var class="var">params</var></dt>
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<dd><p>the params of the current node
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</p>
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</dd>
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<dt><var class="var">layout</var></dt>
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<dd><p>the layout coming into this node
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</p>
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</dd>
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</dl>
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<p><var class="var">pre-layout-handler</var> is expected to use this information to return a
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layout to pass to the kids. The default implementation returns the
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layout given in the arguments.
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</p>
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</dd>
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<dt><var class="var">post-handler</var></dt>
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<dd><p>A function of five arguments:
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</p>
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<dl class="table">
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<dt><var class="var">tag</var></dt>
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<dd><p>the current tag being processed
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</p>
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</dd>
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<dt><var class="var">params</var></dt>
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<dd><p>the params of the current node
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</p>
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</dd>
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<dt><var class="var">layout</var></dt>
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<dd><p>the layout coming into the current node, before any kids were processed
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</p>
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</dd>
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<dt><var class="var">klayout</var></dt>
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<dd><p>the layout after processing all of the children
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</p>
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</dd>
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<dt><var class="var">kids</var></dt>
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<dd><p>the already-processed child nodes
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</p>
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</dd>
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</dl>
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<p><var class="var">post-handler</var> should return two values, the layout to pass to the
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next node and the final tree.
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</p>
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</dd>
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<dt><var class="var">text-handler</var></dt>
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<dd><p><var class="var">text-handler</var> is a function of three arguments:
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</p>
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<dl class="table">
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<dt><var class="var">text</var></dt>
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<dd><p>the string
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</p>
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</dd>
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<dt><var class="var">params</var></dt>
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<dd><p>the current params
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</p>
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</dd>
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<dt><var class="var">layout</var></dt>
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<dd><p>the current layout
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</p>
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</dd>
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</dl>
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<p><var class="var">text-handler</var> should return two values, the layout to pass to the
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next node and the value to which the string should transform.
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</p>
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</dd>
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</dl>
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</dd></dl>
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</div>
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</div>
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<hr>
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<div class="nav-panel">
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<p>
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Next: <a href="SXPath.html">SXPath</a>, Previous: <a href="Transforming-SXML.html">Transforming SXML</a>, Up: <a href="SXML.html">SXML</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
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</div>
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</body>
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</html>
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