/usr/share/doc/libexpat1-dev/expat.html/index.html is in libexpat1-dev 2.0.1-7.2ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/libexpat1-dev/expat.html/reference.html
/usr/share/doc/libexpat1-dev/expat.html/reference.html