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<title>DTD Attributes</title>
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<p>From <b>http://www.w3schools.com</b> (Copyright Refsnes Data)</p>
<h1>DTD - Attributes</h1>
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<p class="intro">In a DTD, attributes are declared with an ATTLIST declaration.</p>
<hr />
<h2>Declaring Attributes</h2>
<p>An
attribute declaration has the following syntax:</p>
<table border="1" width="100%" class="ex" cellspacing="0">
<tr><td width="100%"><pre><!ATTLIST element-name attribute-name attribute-type default-value></pre><pre>DTD example:</pre>
<pre><!ATTLIST payment type CDATA "check"></pre>
<pre>XML example:</pre>
<pre><payment type="check" /></pre></td></tr>
</table>
<p>The <b>attribute-type</b> can be one of the following:</p>
<table border="1" width="100%" class="ex" cellspacing="0">
<tr>
<th width="25%" align="left">Type</th>
<th width="75%" align="left">Description</th>
</tr>
<tr>
<td><p>CDATA</p></td>
<td><p>The value is character data</p></td>
</tr>
<tr>
<td><p>(<i>en1</i>|<i>en2</i>|..)</p></td>
<td><p>The value must be one from an enumerated list</p></td>
</tr>
<tr>
<td><p>ID</p></td>
<td><p>The value is a unique id </p></td>
</tr>
<tr>
<td><p>IDREF</p></td>
<td><p>The value is the id of another element</p></td>
</tr>
<tr>
<td><p>IDREFS</p></td>
<td><p>The value is a list of other ids</p></td>
</tr>
<tr>
<td><p>NMTOKEN</p></td>
<td><p>The value is a valid XML name</p></td>
</tr>
<tr>
<td><p>NMTOKENS</p></td>
<td><p>The value is a list of valid XML names</p></td>
</tr>
<tr>
<td><p>ENTITY</p></td>
<td><p>The value is an entity </p></td>
</tr>
<tr>
<td><p>ENTITIES</p></td>
<td><p>The value is a list of entities</p></td>
</tr>
<tr>
<td><p>NOTATION</p></td>
<td><p>The value is a name of a notation</p></td>
</tr>
<tr>
<td><p>xml:</p></td>
<td><p>The value is a predefined xml value</p></td>
</tr>
</table>
<p>The <b>default-value</b> can be one of the following:</p>
<table border="1" width="100%" class="ex" cellspacing="0">
<tr>
<th width="25%" align="left">Value</th>
<th width="75%" align="left">Explanation</th>
</tr>
<tr>
<td><p><i>value</i></p></td>
<td><p>The default value of the attribute</p></td>
</tr>
<tr>
<td><p>#REQUIRED</p></td>
<td><p>The attribute is required</p></td>
</tr>
<tr>
<td><p>#IMPLIED</p></td>
<td><p>The attribute is not required</p></td>
</tr>
<tr>
<td><p>#FIXED <i>value</i></p></td>
<td><p>The attribute value is fixed</p></td>
</tr>
</table>
<br />
<hr />
<h2>A Default Attribute Value</h2>
<table border="1" width="100%" class="ex" cellspacing="0">
<tr><td width="100%"><pre>DTD:
<!ELEMENT square EMPTY>
<!ATTLIST square width CDATA "0"></pre>
<pre>Valid XML:
<square width="100" /></pre></td></tr>
</table>
<p>In the example above, the "square" element is defined to be an empty element with
a "width" attribute of type CDATA. If no width is specified, it has a default
value of 0.</p>
<hr />
<h2>#REQUIRED</h2>
<h3>Syntax</h3>
<table border="1" width="100%" class="ex" cellspacing="0" id="table1">
<tr><td width="100%"><pre><!ATTLIST element-name attribute-name attribute-type #REQUIRED></pre></td></tr>
</table>
<h3>Example</h3>
<table border="1" width="100%" class="ex" cellspacing="0" id="table2">
<tr><td width="100%"><pre>DTD:
<!ATTLIST person number CDATA #REQUIRED></pre><pre>Valid XML:
<person number="5677" /></pre><pre>Invalid XML:
<person /></pre></td></tr>
</table>
<p>Use the #REQUIRED keyword if you don't have an option for a default value, but
still want to force the attribute to be present.</p>
<hr />
<h2>#IMPLIED</h2>
<h3>Syntax</h3>
<table border="1" width="100%" class="ex" cellspacing="0">
<tr><td width="100%"><pre><!ATTLIST element-name attribute-name attribute-type #IMPLIED></pre></td></tr>
</table>
<h3>Example</h3>
<table border="1" width="100%" class="ex" cellspacing="0">
<tr><td width="100%"><pre>DTD:
<!ATTLIST contact fax CDATA #IMPLIED></pre><pre>Valid XML:
<contact fax="555-667788" /></pre><pre>Valid XML:
<contact /></pre></td></tr>
</table>
<p>Use the #IMPLIED keyword if you don't want to force the author to include an
attribute, and you don't have an option for a default value.</p>
<hr />
<h2>#FIXED</h2>
<h3>Syntax</h3>
<table border="1" width="100%" class="ex" cellspacing="0">
<tr><td width="100%"><pre><!ATTLIST element-name attribute-name attribute-type #FIXED "value"></pre></td></tr>
</table>
<h3>Example</h3>
<table border="1" width="100%" class="ex" cellspacing="0">
<tr><td width="100%"><pre>DTD:
<!ATTLIST sender company CDATA #FIXED "Microsoft"></pre><pre>Valid XML:
<sender company="Microsoft" /></pre><pre>Invalid XML:
<sender company="W3Schools" /></pre></td></tr>
</table>
<p>Use the #FIXED keyword when you want an attribute to have a fixed value
without allowing the author to change it. If an author includes another value,
the XML parser will return an error.</p>
<hr />
<h2>Enumerated Attribute Values</h2>
<h3>Syntax</h3>
<table border="1" width="100%" class="ex" cellspacing="0">
<tr><td width="100%"><pre><!ATTLIST element-name attribute-name (en1|en2|..) default-value></pre></td></tr>
</table>
<h3>Example</h3>
<table border="1" width="100%" class="ex" cellspacing="0" id="table3">
<tr><td width="100%">
<pre>DTD:
<!ATTLIST payment type (check|cash) "cash"></pre>
<pre>XML example:
<payment type="check" />
or
<payment type="cash" /></pre></td></tr>
</table>
<p>Use enumerated attribute values when you want the attribute value to be one of
a fixed set of legal values.</p>
<hr />
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<p>From <b>http://www.w3schools.com</b> (Copyright Refsnes Data)</p>
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