<xsl:for-each-group select="Text" group-by="tokenize(@data,'\s+')">
<xsl:for-each select="current-group()">
<xsl:sort select="current-grouping-key()" lang="cz"/>
<Word title="{@title}" ref="{@ref}">
<xsl:value-of select="."/>
</Word>
</xsl:for-each>
</xsl:for-each-group>

And received the warning:  "Sort key will have no effect because its
value does not depend on the context item"

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