xsltproc does not run on content within xincluded files
When running xsltproc --xinclude, any XSL Transform syntax within the included files is not processed. It seems that the XInclude processing should be done first, and then the XSL Transform operations performed. Instead, the XSLT is performed only on the input file and not the content of the files included by XInclude.
A work-around is to run xmllint --xinclude on the .xslt file first, output the content to a temp file, and then run xsltproc on the temp file.
Test System: CentOS 7.5.1804 amd64 with libxslt-1.1.28-5.el7.x86_64
Edited by Nick Wellnhofer