xsltproc: xsl:import : unable to load urn:docbkx:stylesheet

[anyberry@…]

I have a simple custom xsl stylesheet which has this import:

<xsl:import href="urn:docbkx:stylesheet"/>

(in fact what I'm trying to do is built the maven reference book and the stylesheet is here: ​https://github.com/sonatype/maven-reference-en/blob/master/epub/epub-custom.xsl)

when I run a2x, I get this error:

warning: failed to load external entity "urn:docbkx:stylesheet"
compilation error: file /Users/rasp/git/maven-reference-en/epub/epub-custom.xsl line 7 element import
xsl:import : unable to load urn:docbkx:stylesheet

the actual command is:

xsltproc --stringparam callout.graphics 0 --stringparam navig.graphics 0 --stringparam admon.textlabel 1 --stringparam admon.graphics 0 --stringparam html.stylesheet "epub/epub-custom.css" --stringparam toc.section.depth 1 --stringparam chunk.section.depth 0  "/Users/rasp/git/maven-reference-en/epub/epub-custom.xsl" "/Users/rasp/git/maven-reference-en/target/book-mvnref.xml"

if I run the command without this custom stylesheet, it works properly.

I think this is something that should work out of the box - for some reason the standard stylesheet cannot be found during the import. I haven't figured out how to make this work. yes, I saw Ticket #35303 but that says that docbook-xsl should fix such a problem but it doesn't in my case