<xsl:template match="*">
    <xsl:message>unexpected element encountered: <xsl:value-of select="name()" /></xsl:message>
  </xsl:template>

as always, a match template only executes if you apply templates to a
matching node. that version makes a warning and doesn't process
children. If you want to process children then


  <xsl:template match="*">
    <xsl:message>unexpected element encountered: <xsl:value-of select="name()" /></xsl:message>
<xsl:apply-templates/>
  </xsl:template>


I use either form, depending. If I haven't got round to supporting
mathml yet I'd rather get one warning for each mathml:math element
at the top level of each expression in the document, I don't really want
to be told on every character of every expression that I haven't yet
supported mathml:mi, so I'd use the first form. In other cases, the
second form, processing children is more useful.

Other variants:


  <xsl:template match="*">
    <xsl:message>unexpected element encountered: <xsl:value-of select="name()" /></xsl:message>
    <div class="error">
   <span>unexpected element encountered: <xsl:value-of select="name()" /></span>
<xsl:apply-templates/>
  </div>
  </xsl:template>

so that you not only get a warning, but also a big red block of stuff in
the output.

David

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