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<h1 class="content-header header-section1" id="xgui_expose_dom" itemprop="headline">The DOM tree</h1>
</div></div><p>We will use this XML document for the examples:</p><a name="misc.example.bookXml"></a>

    <div class="code-block role-unspecified">
<pre class="code-block-body">&lt;book&gt;
  &lt;title&gt;Test Book&lt;/title&gt;
  &lt;chapter&gt;
    &lt;title&gt;Ch1&lt;/title&gt;
    &lt;para&gt;p1.1&lt;/para&gt;
    &lt;para&gt;p1.2&lt;/para&gt;
    &lt;para&gt;p1.3&lt;/para&gt;
  &lt;/chapter&gt;
  &lt;chapter&gt;
    &lt;title&gt;Ch2&lt;/title&gt;
    &lt;para&gt;p2.1&lt;/para&gt;
    &lt;para&gt;p2.2&lt;/para&gt;
  &lt;/chapter&gt;
&lt;/book&gt;</pre>    </div>
<p>W3C DOM models an XML document as a tree of nodes. The node tree
        of the above XML can be visualized as:</p>

    <div class="code-block role-unspecified">
<pre class="code-block-body">document
 |
 +- element book
     |
     +- text &quot;\n  &quot;
     |
     +- element title
     |   |
     |   +- text &quot;Test Book&quot;
     |
     +- text &quot;\n  &quot;
     |
     +- element chapter
     |   |
     |   +- text &quot;\n    &quot;
     |   |
     |   +- element title
     |   |   |
     |   |   +- text &quot;Ch1&quot;
     |   |
     |   +- text &quot;\n    &quot;
     |   |
     |   +- element para
     |   |   |
     |   |   +- text &quot;p1.1&quot;
     |   |
     |   +- text &quot;\n    &quot;
     |   |
     |   +- element para
     |   |   |
     |   |   +- text &quot;p1.2&quot;
     |   |
     |   +- text &quot;\n    &quot;
     |   |
     |   +- element para
     |      |
     |      +- text &quot;p1.3&quot;
     |
     +- element
         |
         +- text &quot;\n    &quot;
         |
         +- element title
         |   |
         |   +- text &quot;Ch2&quot;
         |
         +- text &quot;\n    &quot;
         |
         +- element para
         |   |
         |   +- text &quot;p2.1&quot;
         |
         +- text &quot;\n    &quot;
         |
         +- element para
             |
             +- text &quot;p2.2&quot;</pre>    </div>
<p>Note that the disturbing <code class="inline-code">&quot;\n  &quot;</code>-s are the
        line-breaks (indicated here with <code class="inline-code">\n</code>, an escape
        sequence used in FTL string literals) and the indentation spaces
        between the tags.</p><p>Notes on the DOM related terminology:</p><ul>
          <li>
            <p>The topmost node of a tree is called the <strong>root</strong>. In the case of XML documents, it is
            always the "document" node, and not the top-most
            element (<code class="inline-code">book</code> in this example).</p>
          </li>

          <li>
            <p>We say that node B is the <strong>child</strong> of node A, if B is the
            <em>immediate</em> descendant of A. For example, the
            two <code class="inline-code">chapter</code> element nodes are the children of
            the <code class="inline-code">book</code> element node, but the
            <code class="inline-code">para</code> element nodes are not.</p>
          </li>

          <li>
            <p>We say that node A is the <strong>parent</strong> of node B, if A is the
            <em>immediate</em> ascendant of node B, that is, if B
            is the children of A. For example, the <code class="inline-code">book</code>
            element node is the parent of the two <code class="inline-code">chapter</code>
            element nodes, but it is not the parent of the
            <code class="inline-code">para</code> element nodes.</p>
          </li>

          <li>
            <p>There are several kind of components that can occur in XML
            documents, such as elements, text, comments, processing
            instructions, etc. All such components are nodes in the DOM tree,
            so there are element nodes, text nodes, comment nodes, etc. In
            principle, the attributes of elements are also nodes in the tree
            -- they are the children of the element --, but still, usually we
            (and other XML related technologies) exclude them of element
            children. So basically they don&#39;t count as children nodes.</p>
          </li>
        </ul><p>The programmer drops the document node of the DOM tree into the
        FreeMarker data-model, and then the template author can walk the DOM
        tree using that variable as the starting-point.</p><p>The DOM nodes in FTL correspond to <strong>node
        variables</strong>. This is a variable type, similarly to type
        string, number, hash, etc. Node variable type makes it possible for
        FreeMarker to get the parent node and the child nodes of a node. This
        is technically required to allow the template author to navigate
        between the nodes, say, to use the <a href="ref_builtins_node.html">node built-ins</a> or the <a href="ref_directive_visit.html#ref.directive.visit"><code>visit</code></a> and
        <a href="ref_directive_visit.html#ref.directive.recurse"><code>recurse</code></a>
        directives; we will show the usage of these in the further
        chapters.</p><div class="bottom-pagers-wrapper"><div class="pagers bottom"><a class="paging-arrow previous" href="xgui_expose.html"><span>Previous</span></a><a class="paging-arrow next" href="xgui_expose_put.html"><span>Next</span></a></div></div></div></div>      </div>
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