/usr/share/doc/libocamlnet-ocaml-dev/html/api is in libocamlnet-ocaml-doc 4.1.2-3.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/libocamlnet-ocaml-dev/html/../../libocamlnet-ocaml-doc/html-main