You can search for identifiers within the package.
in-package search v0.2.0
devkit.core
Devkit_core.Lwt_engines
module U = ExtUnix.Specific
module Ev = Libevent
class poll : object ... end
type Lwt_engine.engine_id +=
| Engine_id__Devkit_libevent
class libevent : object ... end
libevent-based engine for lwt