Circular import

A stylesheet must not xsl:import or xsl:include, directly or through a chain, a stylesheet that pulls it back — nor import itself. A processor treats this as a static error (XTSE0210) and refuses to compile the stylesheet, so the cycle is never a working design, only a mistake to break.

The linter resolves every @href against the importing file's own directory and matches it to the corpus. A cycle needs every edge in it to resolve within the files being linted, so an href pointing at a library outside the corpus is treated as external and never mistaken for part of a cycle.

Incorrect (a.xsl and b.xsl import each other):

<!-- a.xsl -->
<xsl:stylesheet version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:import href="b.xsl"/>
</xsl:stylesheet>

<!-- b.xsl -->
<xsl:stylesheet version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:import href="a.xsl"/>
</xsl:stylesheet>

Correct — move the shared code into a third module both import, so the graph stays acyclic:

<!-- a.xsl -->
<xsl:stylesheet version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:import href="common.xsl"/>
</xsl:stylesheet>

<!-- b.xsl -->
<xsl:stylesheet version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:import href="common.xsl"/>
</xsl:stylesheet>