/usr/share/sgml/docbook/dtd/xml/4.3 is in docbook-xml 4.5-7.3.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/sgml/docbook/dtd/xml/../../../../xml/docbook/schema/dtd/4.3
/usr/share/sgml/docbook/dtd/xml/../../../../xml/docbook/schema/dtd/4.3