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274 lines
8.7 KiB
HTML
274 lines
8.7 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0//EN">
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<html>
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<head>
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<title>XSLT Templates and Compiling</title>
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<style type="text/css">
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.section {
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background-color: #cfcfcf;
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margin-left: 2em;
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}
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.required {
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font-weight: bold;
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}
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.TODO {
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color: red;
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}
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</style>
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</head>
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<body>
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<h1>XSLT Templates and Compiling</h1>
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<p>This document describes compiling of XSLT stylesheets and the
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evaluation of the result.</p>
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<div>
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<ul>
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<li><a href="#pre">Prerequisites</a></li>
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<li><a href="#comp">Compilation</a></li>
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<li><a href="#eval">Evaluation</a></li>
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</ul>
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</div>
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<h2><a name="pre">Objectives:</a></h2>
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<ul>
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<li>Speed</li>
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<li>Better support for AVTs</li>
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<li>Interruptability of processing</li>
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<li>exclude and alias namespaces</li>
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</ul>
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<h2>Concepts:</h2>
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<div>
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<dl>
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<dt>LRE namespaces</dt>
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<dd>All namespace aliases are merged wit import precedence
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into an array of all namespace ids, which is used to map the
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LRE namespace in the source to the LRE namespace in the
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result. Non-aliased namespaces just have their namespace id
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in that array.</dd>
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</dl>
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</div>
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<h2><a name="comp">Compilation:</a></h2>
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<p>The XSLT specification describes XSLT in terms of the XPath
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datamodel, something pretty close to a DOM. So we talk about the
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input in terms of DOM elements.</p>
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<div>The DOM nodes in a stylesheet get compiled into either
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<ul>
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<li>nothing :-) (stuff like xsl:output),</li>
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<li><code>xslTopElement</code>s or</li>
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<li><code>xslInstruction</code>s.</li>
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</ul>
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The <code>xslInstruction</code>s fall into classes,
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<ol>
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<li>simple instructions,</li>
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<li>utilities (no-op, variable-pop, push-handler),</li>
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<li>branching instructions,</li>
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<li>instructions changing the result handler and</li>
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<li>instructions calling into different
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<code>xslTopElement</code>s.</li>
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</ol>
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</div>
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<h2><a name="eval">How do instructions work?</a></h2>
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<div>The general pattern used to create output from a set of
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instructions is
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<pre>while (instruction) {
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rv = instruction.do(args);
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if (NS_FAILED(rv)) {
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//cleanup
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return rv;
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}
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instruction = instruction.mNext;
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}</pre>
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This says pretty much all about simple and utility instructions.
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</div>
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<h3>Branching instructions</h3>
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<div>see <a href="#choose">xsl:choose</a>. The trailing single
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no-op helps in rejoining the paths, as that no-op can be created
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before the paths and thus easily appended to each end of the
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paths.</div>
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<h3>Instructions that change the output handler</h3>
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<div>These instructions (attribute, comment, pi creating text
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handlers, variable possibly creating a rtf handler) get created
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by inserting a push-handler-instruction into the workflow for
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the start of the element and the XSLT instruction at the
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end. The handler instruction should keep a non-owning reference
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to the push-handler-instruction to get the result and restore
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the previous handler.</div>
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<h3><a name="apply-imports">xsl:apply-imports</a></h3>
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<div class="section">no idea</div>
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<h3><a name="apply-templates">xsl:apply-templates</a></h3>
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<div class="section">
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<dl>
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<dt>members:</dt>
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<dd>
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<dl>
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<dt>select</dt> <dd>node-set-expression</dd>
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<dt>mode</dt> <dd>qname</dd>
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<dt>sorts</dt> <dd>list of xsl:sort elements</dd>
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<dt>params</dt> <dd>list of xsl:with-param elements</dd>
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</dl>
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</dd>
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<dt>do()</dt>
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<dd>set up the params, if any, evaluate the select, create a
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evalContext and push it on the evalContextStack. push the next
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instruction to the instruction return stack. trigger the new
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context (how do we do this?).</dd>
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</dl>
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</div>
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<h3><a name="attribute">xsl:attribute</a></h3>
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<div class="section">
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<dl>
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<dt>members:</dt>
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<dd>
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<dl>
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<dt class="required">name</dt> <dd>AVT with QName value</dd>
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<dt>namespace</dt> <dd>AVT with uri value</dd>
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</dl>
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</dd>
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<dt>do()</dt>
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<dd>the start tag pushes a textValueHandler, the end tag pops
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the value handler and calls the outputhandler::attribute</dd>
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</dl>
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</div>
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<h3><a name="attribute-set">xsl:attribute-set</a> (tle)</h3>
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<div class="section"><span class="TODO">attribute sets are merged,
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we should pay attention that multiple stylesheet compilers
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don't mix their content. Order of attributes is relevant, IMHO.</span>
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<dl>
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<dt>members:</dt>
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<dd>
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<dl>
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<dt class="required">name</dt> <dd>qname</dd>
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<dt>use-attribute-sets</dt> <dd>list of qnames</dd>
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</dl>
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</dd>
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<dt>do()</dt>
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<dd>merging and stuff needed in the global stylesheet object,
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(NOT part of <a href="#import-frame">import frame).</a></dd>
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</dl>
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</div>
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<h3><a name="call-template">xsl:call-template</a></h3>
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<div class="section">
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<dl>
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<dt>members:</dt>
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<dd>
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<dl>
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<dt class="required">name</dt> <dd>qname</dd>
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<dt>with-params</dt> <dd>list of xsl:with-params</dd>
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</dl>
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</dd>
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<dt>do()</dt>
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<dd>push the next instruction onto the instruction return
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stack, lookup the template and set the instruction pointer
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to the called template. Setup the params, if there are. This
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does not change the evalContextStack.
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<div class="issue">Can we cache this? What happens if a
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added stylesheet between two transforms changes which
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stylesheet this qname resolves to?</div></dd>
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</dl>
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</div>
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<h3><a name="choose">xsl:choose</a></h3>
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<div class="section">
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This is a branching instruction with one exit point and several
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conditional entry points (xsl:when) and one default
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(xsl:otherwise). The conditional entry points start with a
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conditionalGotoInstrunction, which jumps to the next entry point
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if they don't succeed. Each of them ends with a gotoInstruction
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that jumps to the end of the xsl:choose (for simplicity in the
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compilation phase, this might be a noopInstruction). The
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xsl:otherwise is just the instructions list of the
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xsl:otherwise, linked to the ending noopInstruction. Note that
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this construct a single instruction list for the complete
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xsl:choose, as the mNext of the final gotos is the next entry
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point. This mNext is only used for iterations, though.
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</div>
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<h3><a name="comment">xsl:comment</a></h3>
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<div class="section">
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<dl>
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<dt>do()</dt>
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<dd>startElement pushes a textHandler, endElement takes the
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value and calls ::comment() in the output handler</dd>
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</dl>
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</div>
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<h3><a name="copy">xsl:copy</a></h3>
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<div class="section">
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<dl>
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<dt>members:</dt>
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<dd></dd>
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<dt>do()</dt>
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<dd>xsl:copy has a <a
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href="#attribute-sets">use-attribute-sets</a> attribute,
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<span class="TODO">TODO</span></dd>
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</dl>
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</div>
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<h3><a name="copy-of">xsl:copy-of</a></h3>
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<div class="section">
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<dl>
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<dt>members:</dt>
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<dd>
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<dl>
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<dt class="required">select</dt>
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<dd>an expression to be added to the result tree</dd>
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</dl>
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</dd>
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<dt>do()</dt>
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<dd>the value of the result is added to the result tree. If
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the result is a RTF, the RTF is just fed into the output
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handler, if the result is not a nodeset, it is converted
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into a string and ::characters is called on the output
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handler. For nodesets, the result is a list of source nodes
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which have to be interpreted, for example thru the
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stylesheet compiler. This has be xslt-blind, that is, xslt
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elements in the source must be treated as LRE elements and
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copied into the result, instead of generating XSLT
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instructions. <span class="TODO">is this all?</span></dd>
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</dl>
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</div>
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<h3><a name="decimal-format">xsl:decimal-format</a> (tle)</h3>
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<div class="section">xsl:decimal-format is stored in the global
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stylesheet object, import precedence <b>does not</b> apply.</div>
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<h3><a name="element">xsl:element</a></h3>
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<div class="section">
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<dl>
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<dt>members:</dt>
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<dd>
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<dl>
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<dt class="required">name</dt> <dd>AVT with QName
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value</dd>
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<dt>namespace</dt> <dd>AVT with URI value</dd>
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</dl>
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</dd>
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<dt>do()</dt>
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<dd>xsl:element has <a
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href="#attribute-sets">attribute-set</a>s, <span
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class="TODO">todo</span>. Other than that, this just
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generates an element. Note that the attributes of this
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element have to be discarded, if the name AVT does not
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evaluate to a QName.</dd>
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</dl>
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</div>
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<h3><a name="fallback">xsl:fallback</a></h3>
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<div class="section"><span class="TODO">do we care?</span></div>
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<h3><a name=""></a></h3>
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<div class="section">
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<dl>
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<dt>members:</dt>
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<dd></dd>
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<dt>do()</dt>
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<dd></dd>
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</dl>
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</div>
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</body>
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</html>
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