The @disable_unused_warnings annotation disables the many OCaml
compiler warnings having to do with something being used (variable,
constructor, declaration, open, rec keyword, etc.). It can be
used at all three annotation scopes:
[@@@disable_unused_warnings][@@disable_unused_warnings][@disable_unused_warnings]
As of OCaml 4.10, it translates [@disable_unused_warnings] to:
[@@@warning "-26-27-32-33-34-35-36-37-38-39-60-66-67"]