/usr/share/doc/docbook-xsl-ns/reference.html is in docbook-xsl-doc-html 1.78.1-1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/docbook-xsl-ns/../docbook-xsl-doc-html/doc
/usr/share/doc/docbook-xsl-ns/../docbook-xsl-doc-html/doc