/usr/share/ is in w3c-dtd-xhtml 1.1-5ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/share/xml/
/usr/share/xml/xhtml/
/usr/share/xml/xhtml/schema/
/usr/share/xml/xhtml/schema/dtd/
/usr/share/xml/xhtml/schema/dtd/1.0/
/usr/share/xml/xhtml/schema/dtd/1.0/xhtml1-frameset.dtd
/usr/share/xml/xhtml/schema/dtd/1.0/xhtml1-strict.dtd
/usr/share/xml/xhtml/schema/dtd/1.0/xhtml1-transitional.dtd
/usr/share/xml/xhtml/schema/dtd/1.0/xhtml-lat1.ent
/usr/share/xml/xhtml/schema/dtd/1.0/xhtml-special.ent
/usr/share/xml/xhtml/schema/dtd/1.0/xhtml-symbol.ent
/usr/share/xml/xhtml/schema/dtd/1.0/catalog
/usr/share/xml/xhtml/schema/dtd/1.0/catalog.xml
/usr/share/xml/xhtml/schema/dtd/1.1/
/usr/share/xml/xhtml/schema/dtd/1.1/xhtml11-flat.dtd
/usr/share/xml/xhtml/schema/dtd/1.1/xhtml11.dtd
/usr/share/xml/xhtml/schema/dtd/1.1/xhtml11-model-1.mod
/usr/share/xml/xhtml/schema/dtd/1.1/catalog
/usr/share/xml/xhtml/schema/dtd/1.1/catalog.xml
/usr/share/xml/xhtml/schema/dtd/basic/
/usr/share/xml/xhtml/schema/dtd/basic/xhtml-basic10-f.dtd
/usr/share/xml/xhtml/schema/dtd/basic/xhtml-basic10.dtd
/usr/share/xml/xhtml/schema/dtd/basic/xhtml-arch-1.mod
/usr/share/xml/xhtml/schema/dtd/basic/xhtml-attribs-1.mod
/usr/share/xml/xhtml/schema/dtd/basic/xhtml-base-1.mod
/usr/share/xml/xhtml/schema/dtd/basic/xhtml-basic-form-1.mod
/usr/share/xml/xhtml/schema/dtd/basic/xhtml-basic-table-1.mod
/usr/share/xml/xhtml/schema/dtd/basic/xhtml-basic10-model-1.mod
/usr/share/xml/xhtml/schema/dtd/basic/xhtml-blkphras-1.mod
/usr/share/xml/xhtml/schema/dtd/basic/xhtml-blkstruct-1.mod
/usr/share/xml/xhtml/schema/dtd/basic/xhtml-charent-1.mod
/usr/share/xml/xhtml/schema/dtd/basic/xhtml-datatypes-1.mod
/usr/share/xml/xhtml/schema/dtd/basic/xhtml-framework-1.mod
/usr/share/xml/xhtml/schema/dtd/basic/xhtml-hypertext-1.mod
/usr/share/xml/xhtml/schema/dtd/basic/xhtml-image-1.mod
/usr/share/xml/xhtml/schema/dtd/basic/xhtml-inlphras-1.mod
/usr/share/xml/xhtml/schema/dtd/basic/xhtml-inlstruct-1.mod
/usr/share/xml/xhtml/schema/dtd/basic/xhtml-link-1.mod
/usr/share/xml/xhtml/schema/dtd/basic/xhtml-list-1.mod
/usr/share/xml/xhtml/schema/dtd/basic/xhtml-meta-1.mod
/usr/share/xml/xhtml/schema/dtd/basic/xhtml-notations-1.mod
/usr/share/xml/xhtml/schema/dtd/basic/xhtml-object-1.mod
/usr/share/xml/xhtml/schema/dtd/basic/xhtml-param-1.mod
/usr/share/xml/xhtml/schema/dtd/basic/xhtml-qname-1.mod
/usr/share/xml/xhtml/schema/dtd/basic/xhtml-struct-1.mod
/usr/share/xml/xhtml/schema/dtd/basic/xhtml-text-1.mod
/usr/share/xml/xhtml/schema/dtd/basic/catalog
/usr/share/xml/xhtml/schema/dtd/basic/catalog.xml
/usr/share/xml/xhtml/schema/dtd/catalog
/usr/share/xml/xhtml/schema/dtd/catalog.xml
/usr/share/xml/entities/
/usr/share/xml/entities/xhtml/
/usr/share/xml/entities/xhtml/catalog.xml
/usr/share/doc/
/usr/share/doc/w3c-dtd-xhtml/
/usr/share/doc/w3c-dtd-xhtml/README.Debian
/usr/share/doc/w3c-dtd-xhtml/copyright
/usr/share/doc/w3c-dtd-xhtml/examples/
/usr/share/doc/w3c-dtd-xhtml/examples/Makefile
/usr/share/doc/w3c-dtd-xhtml/examples/xhtml-1.0-frameset.xml
/usr/share/doc/w3c-dtd-xhtml/examples/xhtml-1.0-strict.xml
/usr/share/doc/w3c-dtd-xhtml/examples/xhtml-1.0-transitional.xml
/usr/share/doc/w3c-dtd-xhtml/changelog.Debian.gz
/usr/share/xml/xhtml/schema/dtd/1.0/xhtml1.dcl
/usr/share/xml/xhtml/schema/dtd/1.1/xml1.dcl
/usr/share/xml/xhtml/schema/dtd/1.1/xml1n.dcl
/usr/share/xml/xhtml/schema/dtd/basic/xml1.dcl
/usr/share/xml/entities/xhtml/xhtml-lat1.ent
/usr/share/xml/entities/xhtml/xhtml-special.ent
/usr/share/xml/entities/xhtml/xhtml-symbol.ent