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<h1>DTD - Elements</h1>
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<p class="intro">In a DTD, elements are declared with an ELEMENT declaration.</p>
<hr />
<h2>Declaring Elements</h2>
<p>In a DTD, XML elements are declared with an element
declaration with the following syntax:</p>
<table border="1" width="100%" class="ex" cellspacing="0">
<tr><td width="100%"><pre><!ELEMENT element-name category>
or
<!ELEMENT element-name (element-content)></pre></td></tr>
</table><br />
<hr />
<h2>Empty Elements</h2>
<p>Empty elements are declared with the category keyword EMPTY:</p>
<table border="1" width="100%" class="ex" cellspacing="0">
<tr><td width="100%"><pre><!ELEMENT element-name EMPTY></pre>
<pre>Example:</pre><pre><!ELEMENT br EMPTY></pre><pre>XML example:</pre><pre><br /></pre></td></tr>
</table>
<br />
<hr />
<h2>Elements with Parsed Character Data</h2>
<p>Elements with only parsed character data are declared with #PCDATA inside parentheses:</p>
<table border="1" width="100%" class="ex" cellspacing="0">
<tr><td width="100%"><pre><!ELEMENT element-name (#PCDATA)></pre>
<pre>Example:</pre><pre><!ELEMENT from (#PCDATA)></pre></td></tr>
</table>
<br />
<hr />
<h2>Elements with any Contents</h2>
<p>Elements declared with the category keyword ANY, can contain any combination
of parsable data:</p>
<table border="1" width="100%" class="ex" cellspacing="0">
<tr><td width="100%"><pre><!ELEMENT element-name ANY></pre><pre>Example:</pre><pre><!ELEMENT note ANY></pre></td></tr>
</table>
<br />
<hr />
<h2>Elements with Children (sequences)</h2>
<p>Elements with one or more children are declared with the name of the children elements inside
parentheses:</p>
<table border="1" width="100%" class="ex" cellspacing="0">
<tr><td width="100%"><pre><!ELEMENT element-name (child1)>
or
<!ELEMENT element-name (child1,child2,...)></pre><pre>Example:</pre><pre><!ELEMENT note (to,from,heading,body)></pre></td></tr>
</table>
<p>
When children are declared in a sequence separated by commas, the children must
appear in the same sequence in the document. In a full declaration, the children must also be declared, and the children can also have children.
The full declaration of the "note" element is:
</p>
<table border="1" width="100%" class="ex" cellspacing="0">
<tr><td width="100%"><pre><!ELEMENT note (to,from,heading,body)>
<!ELEMENT to (#PCDATA)>
<!ELEMENT from (#PCDATA)>
<!ELEMENT heading (#PCDATA)>
<!ELEMENT body (#PCDATA)></pre></td></tr>
</table>
<br />
<hr />
<h2>Declaring Only One Occurrence of an Element </h2>
<table border="1" width="100%" class="ex" cellspacing="0">
<tr><td width="100%"><pre><!ELEMENT element-name (child-name)></pre><pre>Example:</pre><pre><!ELEMENT note (message)></pre></td></tr>
</table>
<p>The example above declares that the child element "message" must occur
once, and only once inside the "note" element.</p>
<hr />
<h2>Declaring Minimum One Occurrence of an Element</h2>
<table border="1" width="100%" class="ex" cellspacing="0">
<tr><td width="100%"><pre><!ELEMENT element-name (child-name+)></pre><pre>Example:</pre><pre><!ELEMENT note (message+)></pre></td></tr>
</table>
<p>The + sign in the example above declares that the child element "message" must occur
one or more times inside the "note" element.</p>
<hr />
<h2>Declaring Zero or More Occurrences of an Element </h2>
<table border="1" width="100%" class="ex" cellspacing="0">
<tr><td width="100%"><pre><!ELEMENT element-name (child-name*)></pre><pre>Example:</pre><pre><!ELEMENT note (message*)></pre></td></tr>
</table>
<p>The * sign in the example above declares that the child element "message" can occur
zero or more times inside the "note" element.</p>
<hr />
<h2>Declaring Zero or One Occurrences of an Element </h2>
<table border="1" width="100%" class="ex" cellspacing="0">
<tr><td width="100%"><pre><!ELEMENT element-name (child-name?)></pre><pre>Example:</pre><pre><!ELEMENT note (message?)></pre></td></tr>
</table>
<p>The ? sign in the example above declares that the child element "message" can occur
zero or one time inside the "note" element.</p>
<hr />
<h2>Declaring either/or Content</h2>
<table border="1" width="100%" class="ex" cellspacing="0">
<tr><td width="100%">
<pre>Example:</pre><pre><!ELEMENT note (to,from,header,(message|body))></pre></td></tr>
</table>
<p>The example above declares that the "note" element must contain a "to" element, a
"from"
element, a "header" element, and either a "message" or a "body" element.</p>
<hr />
<h2>Declaring Mixed Content</h2>
<table border="1" width="100%" class="ex" cellspacing="0">
<tr><td width="100%"><pre>Example:</pre><pre><!ELEMENT note (#PCDATA|to|from|header|message)*></pre></td></tr>
</table>
<p>The example above declares that the "note" element can contain zero
or more occurrences of parsed character data, "to", "from", "header", or "message" elements.</p>
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