diff --git a/src/actor.rs b/src/actor.rs
index 1b07fa9..dcfa9d3 100644
--- a/src/actor.rs
+++ b/src/actor.rs
@@ -590,10 +590,34 @@ pub trait ApActorExt<Inner>: AsApActor<Inner> {
     }
 }
 
+/// The ActivityStreams Application type
+///
+/// This is just an alias for `Object<ApplicationType>` because there's no fields inherent to
+/// Application that aren't already present on an Object.
 pub type Application = Object<ApplicationType>;
+
+/// The ActivityStreams Group type
+///
+/// This is just an alias for `Object<GroupType>` because there's no fields inherent to
+/// Group that aren't already present on an Object.
 pub type Group = Object<GroupType>;
+
+/// The ActivityStreams Organization type
+///
+/// This is just an alias for `Object<OrganizationType>` because there's no fields inherent to
+/// Organization that aren't already present on an Object.
 pub type Organization = Object<OrganizationType>;
+
+/// The ActivityStreams Person type
+///
+/// This is just an alias for `Object<PersonType>` because there's no fields inherent to
+/// Person that aren't already present on an Object.
 pub type Person = Object<PersonType>;
+
+/// The ActivityStreams Service type
+///
+/// This is just an alias for `Object<ServiceType>` because there's no fields inherent to
+/// Service that aren't already present on an Object.
 pub type Service = Object<ServiceType>;
 
 /// Define activitypub properties for the Actor type as described by the Activity Pub vocabulary.