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<h1>Variable References</h1>
<p>The value of a variable (local or global variable, local or global parameter) may be referred to
using the construct <code>$<i>name</i></code>, where <i>name</i> is the variable name.</p>
<p>The variable is always bound at the textual place where the expression containing it appears;
for example a variable used within an <code>xsl:attribute-set</code> must be in scope at the point where the
attribute-set is defined, not the point where it is used.</p>
<p>A variable may be declared to be of a particular type, for example it may be constrained to
be an integer, or a sequence of strings, or an attribute node. In a schema-aware environment, this
may also be a reference to a user-defined type in a schema. If there is no type declared for the variable,
it may take a value of any data type, and in general it is not possible to
determine its data type statically.</p>
<p>It is an error to refer to a variable that has not been declared.</p>
<p>Starting with XPath 2.0, variables (known as range variables) may be declared within
an XPath expression, not only using <code>xsl:variable</code> elements in an XSLT stylesheet. The
expressions that declare variables are the <code>for</code>, <code>some</code>, and <code>every</code>
expressions. In XQuery, variables can also be declared in a <code>let</code> or <code>typeswitch</code>
expression, as well as in the signature of a user-written function.</p>
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