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The XPath specification defines quite a few addressing mechanisms, and they can be combined in many different ways. As a result, XPath delivers a lot of expressive power for a relatively simple specification. This section illustrates two more interesting combinations:
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<a name="wp64405"> </a><div class="pSmartList1"><li><code class="cCode">LIST[@type=&quot;ordered&quot;][3]</code>--selects all <code class="cCode">LIST</code> elements of type &quot;<code class="cCode">ordered</code>&quot;, and returns the third.</li></div>
<a name="wp64406"> </a><div class="pSmartList1"><li><code class="cCode">LIST[3][@type=&quot;ordered&quot;]</code>--selects the third <code class="cCode">LIST</code> element, but only if it is of type &quot;<code class="cCode">ordered</code>&quot;.</li></div>
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<a name="wp64407"> </a><p class="pNote">
Note: Many more combinations of address operators are listed in section 2.5 of the <a  href="http://www.w3.org/TR/xpath" target="_blank">XPath Specification</a>. This is arguably the most useful section of the spec for defining an XSLT transform.
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<hr><a name="wp64408"> </a><h3 class="pHeading2">
Wildcards
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<a name="wp64409"> </a><p class="pBody">
By definition, an unqualified XPath expression selects a set of XML nodes that matches that specified pattern. For example, <code class="cCode">/HEAD</code> matches all top-level <code class="cCode">HEAD</code> entries, while <code class="cCode">/HEAD[1]</code> matches only the first. <a  href="JAXPXSLT3.html#wp76893">Table 7-1</a> lists the wildcards that can be used in XPath expressions to broaden the scope of the pattern matching.</p><div align="left">
<table border="1" summary="XPath Wildcards" id="wp76893">
  <caption><a name="wp76893"> </a><div class="pTableTitle">
Table 7-1   XPath Wildcards
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  <tr align="center">    <th><a name="wp76897"> </a><div class="pCellHeading">
Wildcard
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    <th><a name="wp76899"> </a><div class="pCellHeading">
Meaning
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<code class="cCode">* </code>
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    <td><a name="wp76903"> </a><div class="pCellBody">
Matches any element node (not attributes or text).
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<code class="cCode">node()</code>
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    <td><a name="wp76907"> </a><div class="pCellBody">
Matches any node of any kind: element node, text node, attribute node, processing instruction node, namespace node, or comment node.
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  <tr align="left">    <td><a name="wp76909"> </a><div class="pCellBody">
<code class="cCode">@*</code>
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    <td><a name="wp76911"> </a><div class="pCellBody">
Matches any attribute node.
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<a name="wp76866"> </a><p class="pBody">
In the project database example, for instance, <code class="cCode">/*PERSON[.=&quot;Fred&quot;]</code> matches any <code class="cCode">PROJECT</code> or <code class="cCode">ACTIVITY</code> element that names Fred. 
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<a name="wp64429"> </a><h3 class="pHeading2">
Extended-Path Addressing
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<a name="wp64430"> </a><p class="pBody">
So far, all of the patterns we've seen have specified an exact number of levels in the hierarchy. For example,<code class="cCode"> /HEAD</code> specifies any <code class="cCode">HEAD</code> element at the first level in the hierarchy, while <code class="cCode">/*/*</code> specifies any element at the second level in the hierarchy. To specify an indeterminate level in the hierarchy, use a double forward slash (<code class="cCode">//</code>). For example, the XPath expression <code class="cCode">//PARA</code> selects all <code class="cCode">paragraph</code> elements in a document, wherever they may be found. 
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<a name="wp64431"> </a><p class="pBody">
The <code class="cCode">//</code> pattern can also be used within a path. So the expression <code class="cCode">/HEAD/LIST//PARA</code> indicates all paragraph elements in a subtree that begins from <code class="cCode">/HEAD/LIST</code>.
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<a name="wp64432"> </a><h3 class="pHeading2">
XPath Data Types and Operators
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<a name="wp64433"> </a><p class="pBody">
XPath expressions yield either a set of nodes, a string, a boolean (true/false value), or a number. <a  href="JAXPXSLT3.html#wp76971">Table 7-2</a> lists the operators that can be used in an Xpath expression</p><div align="left">
<table border="1" summary="XPath Operators" id="wp76971">
  <caption><a name="wp76971"> </a><div class="pTableTitle">
Table 7-2   XPath Operators
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Operator
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    <th><a name="wp76977"> </a><div class="pCellHeading">
Meaning
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<code class="cCode">|</code>
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    <td><a name="wp76981"> </a><div class="pCellBody">
Alternative. For example, <code class="cCode">PARA|LIST</code> selects all <code class="cCode">PARA</code> and <code class="cCode">LIST</code> elements.
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  <tr align="left">    <td><a name="wp76983"> </a><div class="pCellBody">
<code class="cCode">or, and</code>
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    <td><a name="wp76985"> </a><div class="pCellBody">
Returns the or/and of two boolean values.
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<code class="cCode">=, !=</code>
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    <td><a name="wp77048"> </a><div class="pCellBody">
Equal or not equal, for booleans, strings, and numbers. 
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<code class="cCode">&lt;, &gt;, &lt;=, &gt;=</code>
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    <td><a name="wp76993"> </a><div class="pCellBody">
Less than, greater than, less than or equal to, greater than or equal to--for numbers.
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 <code class="cCode">+, -, *, div, mod</code>
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    <td><a name="wp76997"> </a><div class="pCellBody">
Add, subtract, multiply, floating-point divide, and modulus (remainder) operations (e.g. 6 mod 4 = 2)
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</table>
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<a name="wp64460"> </a><p class="pBody">
Finally, expressions can be grouped in parentheses, so you don't have to worry about operator precedence. 
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<a name="wp67633"> </a><p class="pNote">
Note: &quot;Operator precedence&quot; is a term that answers the question, &quot;If you specify <code class="cCode">a + b * c</code>, does that mean <code class="cCode">(a+b) * c</code> or <code class="cCode">a + (b*c)</code>?&quot;. (The operator precedence is roughly the same as that shown in the table.)
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<hr><a name="wp64461"> </a><h3 class="pHeading2">
String-Value of an Element
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<a name="wp64462"> </a><p class="pBody">
Before continuing, it's worthwhile to understand how the string-value of a more complex element is determined. We'll do that now.
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<a name="wp64463"> </a><p class="pBody">
The string-value of an element is the concatenation of all descendent text nodes, no matter how deep. So, for a &quot;mixed-model&quot; XML data element like this:
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&lt;PARA&gt;This paragraph contains a &lt;B&gt;bold&lt;/B&gt; word&lt;/PARA&gt;<a name="wp64464"> </a>
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<a name="wp64465"> </a><p class="pBody">
The string-value of <code class="cCode">&lt;PARA&gt;</code> is &quot;This paragraph contains a bold word&quot;. In particular, note that <code class="cCode">&lt;B&gt;</code> is a child of <code class="cCode">&lt;PARA&gt;</code> and that the text contained in all children is concatenated to form the string-value. 
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<a name="wp64466"> </a><p class="pBody">
Also, it is worth understanding that the text in the abstract data model defined by XPath is fully normalized. So whether the XML structure contains the entity reference <code class="cCode">&amp;lt;</code> or &quot;<code class="cCode">&lt;</code>&quot; in a CDATA section, the element's string-value will contain the &quot;<code class="cCode">&lt;</code>&quot; character. Therefore, when generating HTML or XML with an XSLT stylesheet, occurrences of &quot;<code class="cCode">&lt;</code>&quot; will have to be converted to <code class="cCode">&amp;lt;</code> or enclosed in a CDATA section. Similarly, occurrences of &quot;<code class="cCode">&amp;</code>&quot; will need to be converted to <code class="cCode">&amp;amp;</code>.
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<a name="wp64467"> </a><h3 class="pHeading2">
XPath Functions