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Defining the XSLT Context for XPath Expressions (Windows CE 5.0)

Windows CE 5.0
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At run-time, templates in a style sheet are associated with specific source nodes, starting with the document root node that is associated with the root template (match="/"). Within the template, the associated source node is referred to as the current node. The current node defines a context for evaluating XPath expressions within the template.

XPath expressions are accepted as attribute values for <xsl:value-of>, <xsl:for-each>, <xsl:apply-templates>, <xsl:if>, <xsl:when>, <xsl:copy-of>, <xsl:param>, <xsl:sort>, <xsl:variable>, <xsl:with-param>, and <xsl:template>. The attribute names define how the context for the query is determined and whether it results in a new context.

Select Expressions

The <xsl:value-of>, <xsl:for-each>, <xsl:copy-of>, <xsl:param>, <xsl:sort>, <xsl:variable>, <xsl:with-param>, and <xsl:apply-templates> elements have a select attribute. This expression is evaluated relative to the template's current node. In <xsl:for-each> or <xsl:apply-templates>, the select returns a node-set, and each node in this set becomes the current node for further queries within it.

<TABLE BORDER="1">
  <xsl:for-each select="invoices/invoice">
    <TR>
      <TD>Invoice #<xsl:value-of select="@id"/></TD>
    </TR>
    <xsl:for-each select="items/item">
      <TR>
        <TD><xsl:value-of select="qty"/></TD>
        <TD><xsl:value-of select="description"/></TD>
        <TD>$<xsl:value-of select="price"/></TD>
      </TR>
    </xsl:for-each>
  </xsl:for-each>
</TABLE>

The first <xsl:for-each> selects a set of "invoice" elements, each of which becomes the context for the "items/item" query. Each "item", in turn, becomes the context for the various queries in the <xsl:value-of> elements.

Each node selected by <xsl:apply-templates> is associated with a template and thus, becomes the current node for the template.

Because each expression defines a new context, a set of nested queries, such as those in the preceding example, produces a set or "path" of context nodes active at one time.

Test Boolean Expressions

The conditional elements <xsl:if> and <xsl:when> do not define a new context for queries within themselves because they do not actually select new nodes. They just test to make sure the nodes are there.

<TABLE>
  <xsl:for-each select="items/item">
    <TR>
      <TD>
        <xsl:value-of select="qty"/>
      </TD>
      <TD>
        <xsl:value-of select="description"/>
      </TD>
      <TD>
        $<xsl:value-of select="price"/>
      </TD>
      <TD> <!-- 10% volume discount -->
        <xsl:if test="qty[.>=10]">
          <xsl:for-each select="price">
            <xsl:value-of select="formatNumber(.*.10, '$#,##0.00')"/>
          </xsl:for-each>
        </xsl:if>
      </TD>
      <TD STYLE="text-align:right"> <!-- line total -->
        <xsl:value-of select="formatNumber(user:lineTotal(.), '$#,##0.00')"/> 
      </TD>
    </TR>
  </xsl:for-each>
</TABLE>

In this example you can see that the <xsl:for-each select="price"> query is relative to "item" elements, despite the intervening conditional that tests the "qty" value.

Match Patterns

The <xsl:template> element has a match attribute that accepts a pattern for the purposes of matching templates to specific elements; there is no fixed context for a query in this case. For more information, see Authoring Match Patterns.

See Also

XPath


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