Saxon » SaxonJS

SaxonJS provides an XSLT 3.0 processor that supports XSLT 1.0 backwards compatibility mode.

The fact that something is an error in 1.0 does not make it an error when running 3.0-in-1.0-compatibility-mode.

The semantics of a[.=current()] are well defined in 3.0 (in fact, in 2.0); as you say, the predicate is vacuous. This would not be the case if you wrote, for example

match="a[../@class=current()/@class]"

which would match any a element having the same @class as its parent. Or for something that it's hard to do without current():

match="a[@class=current()/@class]//b"

which matches any b element that has an ancestor a element with a matching @class attribute. (current() in a pattern always refers to the node you are trying to match)`

Michael Kay wrote in #note-1:

SaxonJS provides an XSLT 3.0 processor that supports XSLT 1.0 backwards compatibility mode.

The fact that something is an error in 1.0 does not make it an error when running 3.0-in-1.0-compatibility-mode.

"Backwards compatibility mode" can also change the interpretation of a non-erroneous XSL 1.0 transformation. Example:

The built-in templates used by SaxonJS in an XSL 1.0 transformation pass on parameters so that

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0">
  <xsl:template match="/">
    <xsl:apply-templates select="/" mode="a">
      <xsl:with-param name="b">X</xsl:with-param>
    </xsl:apply-templates>
  </xsl:template>
  <xsl:template match="*" mode="a">
    <xsl:param name="b"/>
    <xsl:value-of select="$b"/>
  </xsl:template>
</xsl:stylesheet>

outputs an X (for any source document).

A strict XSLT 1.0 implementation would output nothing, because the built-in template for the root node would invoke the second template without parameter b.

Yes, that's correct. An XSLT 3.0 processor running in backwards compatibility mode will not always produce the same results as an XSLT 1.0 processor.

This particular change is documented in clause 4 of section J.1.4 of the XSLT 2.0 specification. In this particular case an XSLT 2.0 (or 3.0) processor passes on parameters whether or not the stylesheet version is set to 1.0.