Of course, the forward slash characters are the ones to be used, i.e.
<xsl:import href="..\..\..\Dependencies\XSL\xsl\htmlhelp\htmlhelp.xsl"/>
is incorrect, no need to track this track.
, " URI" ( RFC 2396) , . , , URI, xslt.
XSLT 2.0, fn: base-uri(), , URI , .