You can search for identifiers within the package.
in-package search v0.2.0
type t = Unix.open_flag =
| O_RDONLY
| O_WRONLY
| O_RDWR
| O_NONBLOCK
| O_APPEND
| O_CREAT
| O_TRUNC
| O_EXCL
| O_NOCTTY
| O_DSYNC
| O_SYNC
| O_RSYNC
| O_SHARE_DELETE
| O_CLOEXEC
val sexp_of_t : t -> Sexplib.Sexp.t