/usr/lib/ghc-doc/hoogle/libghc-hxt-regex-xmlschema-doc.txt is in libghc-hxt-regex-xmlschema-doc 9.2.0.2-4build1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/ghc-doc/hoogle/../../../share/doc/libghc-hxt-regex-xmlschema-doc/html/hxt-regex-xmlschema.txt