You can search for identifiers within the package.
in-package search v0.2.0
type _ domain = private
| Unix : [ `Unix ] domain
| Inet : [ `Inet ] domain
| Inet6 : [ `Inet6 ] domain
type unix = [ `Unix ] domain
type inet = [ `Inet ] domain
type inet6 = [ `Inet6 ] domain
val unix : unix
val inet : inet
val inet6 : inet6
type 'a typ = [< `Stream | `Dgram | `Raw | `Seqpacket ] as 'a
val stream : [ `Stream ]
val dgram : [ `Dgram ]
val raw : [ `Raw ]
val seqpacket : [ `Seqpacket ]
type (_, _) t
val create : ?proto:int -> 'a domain -> 'b typ -> ('a domain, 'b typ) t
val to_fd : (_ domain, _ typ) t -> Unix.file_descr