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<h1>xsl:for-each-group</h1>
<p>The <code>xsl:for-each-group</code> element selects a sequence of nodes and/or atomic
values and organizes them into subsets called groups. There are four possible ways of defining the
grouping:</p>
<ul>
<li content="para">
<p>
<b>group-by:</b> This groups together all items having the same value for a grouping key.
The grouping key may have multiple values (a sequence of values) in which case the item is added
to more than one group.</p>
</li>
<li content="para">
<p>
<b>group-adjacent:</b> This groups together all items having the same value for a grouping key,
provided that they are also adjacent in the input sequence. This is useful when you need to wrap a
new element around a sequence of related elements in the source documents, for example a consecutive
sequence of <code><bullet></code> elements. In this case the grouping key must be single-valued.</p>
</li>
<li content="para">
<p>
<b>group-starting-with:</b> This processes the items in the supplied sequence in turn, starting
a new group whenever one of the items matches a specified pattern. This is useful, for example,
when matching an <code><h2></code> element and its following <code><p></code>
elements.</p>
</li>
<li content="para">
<p>
<b>group-ending-with:</b> This processes the items in the supplied sequence in turn, closing
the current group whenever one of the items matches a specified pattern. This is useful
when matching a sequence of items in which the last item in the group carries some distinguishing
attribute such as <code>continued="no"</code>.</p>
</li>
</ul>
<p>Saxon implements the <code>xsl:for-each-group</code> instruction in full.
For examples of using the instruction, see
<a href="http://www.w3.org/TR/xslt20/#grouping" class="bodylink">the XSLT 2.0 specification</a>.</p>
<p>In XSLT 3.0, the capabilities of the <code>xsl:for-each-group</code> instruction
are extended by virtue of the fact that the pattern used in <code>group-starting-with</code>
or <code>group-ending-with</code> can now match atomic values as well as nodes.</p>
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