Modern construct in a 1.0 stylesheet

A stylesheet that declares version="1.0" must run on an XSLT 1.0 processor, where the instructions and syntax introduced in XSLT 2.0 simply do not exist. A 1.0 processor (or Saxon-HE in 1.0 mode) rejects them, so a declared-1.0 stylesheet that reaches for a 2.0 construct is a real portability bug — it will not run where its own version attribute promises it will.

This check flags a curated set of 2.0-only XSLT instructions — xsl:for-each-group, xsl:sequence, xsl:analyze-string, xsl:next-match, xsl:perform-sort, xsl:namespace, xsl:character-map, xsl:result-document, xsl:import-schema — and the 2.0 as sequence-type attribute on any other XSLT element, whenever the version in force over that element is earlier than 2.0. Only elements in the XSLT namespace are examined for @as, so a literal result element that legitimately carries an as attribute — <link rel="preload" as="script"/> in HTML output — is never mistaken for the sequence-type attribute.

xsl:function is deliberately left out: it has its own check, function-use-in-xslt-1, which asks the same question of the same version. The 2.0 functions and operators that live inside XPath expressions (lower-case(), matches(), ||, if/then/else, *:name) are not flagged yet — telling a reserved 2.0 built-in from a user-namespaced call needs token-aware parsing, which waits on the full-fidelity parser (#228).

Either rewrite the construct with its 1.0 equivalent — a Muenchian grouping key for xsl:for-each-group, a named template for xsl:sequence — or raise the stylesheet to version="2.0". Because that rewrite is structural, this check reports without a --fix.

Incorrect:

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0">
  <xsl:template match="/objects">
    <xsl:for-each-group select="*" group-by="@key">
      <xsl:sequence select="current-group()"/>
    </xsl:for-each-group>
  </xsl:template>
</xsl:stylesheet>

Correct:

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="2.0">
  <xsl:template match="/objects">
    <xsl:for-each-group select="*" group-by="@key">
      <xsl:sequence select="current-group()"/>
    </xsl:for-each-group>
  </xsl:template>
</xsl:stylesheet>