/usr/share/sgml/docbook/dtd/4.3/ is in docbook 4.5-5.1.
This file is owned by root:root, with mode 0o755.
..
/usr/share/sgml/docbook/dtd/4.3/calstblx.dtd
/usr/share/sgml/docbook/dtd/4.3/catalog
/usr/share/sgml/docbook/dtd/4.3/dbcentx.mod
/usr/share/sgml/docbook/dtd/4.3/dbgenent.mod
/usr/share/sgml/docbook/dtd/4.3/dbhierx.mod
/usr/share/sgml/docbook/dtd/4.3/dbnotnx.mod
/usr/share/sgml/docbook/dtd/4.3/dbpoolx.mod
/usr/share/sgml/docbook/dtd/4.3/docbook.cat
/usr/share/sgml/docbook/dtd/4.3/docbook.dcl
/usr/share/sgml/docbook/dtd/4.3/docbook.dtd
/usr/share/sgml/docbook/dtd/4.3/docbookx.dtd
/usr/share/sgml/docbook/dtd/4.3/htmltblx.mod
/usr/share/sgml/docbook/dtd/4.3/soextblx.dtd