An xsl:import or xsl:include whose href names a missing file stops the
whole stylesheet from compiling (static error XTSE0165). It usually means the
module was renamed or moved. A relative href resolves against the directory
of the stylesheet holding it.
Incorrect, where the module has moved to lib/:
<xsl:stylesheet version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:import href="common.xsl"/>
</xsl:stylesheet>
Correct:
<xsl:stylesheet version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:import href="lib/common.xsl"/>
</xsl:stylesheet>
Only a relative href is checked, and not on an import under an xml:base or
a use-when, which may move or skip the module.