--fix-suggestions rewrites this one, and a plain --fix leaves it alone: the correction changes what the stylesheet does, or is one of several the check would accept.

Leaking result namespace

A literal result element copies every namespace in scope on the stylesheet into the result tree, unless the prefix is excluded. So a prefix declared only for the stylesheet's own logic — xs for a sequence type in as="xs:integer", a helper my/eo called from a select — is serialized onto output elements it never names. xsl:element does not do this, so the leak appears precisely when a static xsl:element is rewritten as a literal result element.

List such a prefix in exclude-result-prefixes on the stylesheet root: the prefix stays available to expressions and to name declarations, but is dropped from the serialized output. This differs from a redundant declaration (a prefix used nowhere, which should be removed): the prefix here is used, just not by any result element.

Incorrect:

<xsl:stylesheet version="2.0"
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
  xmlns:xs="http://www.w3.org/2001/XMLSchema">
  <xsl:template match="/">
    <object>
      <xsl:value-of select="1 cast as xs:integer"/>
    </object>
  </xsl:template>
</xsl:stylesheet>
<!-- <object> is serialized as <object xmlns:xs="..."> -->

Correct:

<xsl:stylesheet version="2.0"
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
  xmlns:xs="http://www.w3.org/2001/XMLSchema"
  exclude-result-prefixes="xs">
  <xsl:template match="/">
    <object>
      <xsl:value-of select="1 cast as xs:integer"/>
    </object>
  </xsl:template>
</xsl:stylesheet>