diff --git a/actix-service/src/lib.rs b/actix-service/src/lib.rs
index cc82bfa6..3db2bcc5 100644
--- a/actix-service/src/lib.rs
+++ b/actix-service/src/lib.rs
@@ -53,8 +53,14 @@ use self::ready::{err, ok, ready, Ready};
 /// async fn(Request) -> Result<Response, Err>
 /// ```
 ///
-/// The `Service` trait just generalizes this form where each parameter is described as an
-/// associated type on the trait. Services can also have mutable state that influence computation.
+/// The `Service` trait just generalizes this form. Requests are defined as a generic type parameter
+/// and responses and other details are defined as associated types on the trait impl. Notice that
+/// this design means that services can receive many request types and converge them to a single
+/// response type.
+///
+/// Services can also have mutable state that influence computation by using a `Cell`, `RefCell`
+/// or `Mutex`. Services intentionally do not take `&mut self` to reduce over-head in the
+/// common cases.
 ///
 /// `Service` provides a symmetric and uniform API; the same abstractions can be used to represent
 /// both clients and servers. Services describe only _transformation_ operations which encourage
@@ -64,8 +70,7 @@ use self::ready::{err, ok, ready, Ready};
 /// ```ignore
 /// struct MyService;
 ///
-/// impl Service for MyService {
-///      type Request = u8;
+/// impl Service<u8> for MyService {
 ///      type Response = u64;
 ///      type Error = MyError;
 ///      type Future = Pin<Box<Future<Output=Result<Self::Response, Self::Error>>>>;
@@ -81,6 +86,9 @@ use self::ready::{err, ok, ready, Ready};
 ///
 /// ```ignore
 /// async fn my_service(req: u8) -> Result<u64, MyError>;
+///
+/// let svc = fn_service(my_service)
+/// svc.call(123)
 /// ```
 pub trait Service<Req> {
     /// Responses given by the service.
@@ -144,7 +152,7 @@ pub trait ServiceFactory<Req> {
     /// Errors potentially raised while building a service.
     type InitError;
 
-    /// The future of the `Service` instance.
+    /// The future of the `Service` instance.g
     type Future: Future<Output = Result<Self::Service, Self::InitError>>;
 
     /// Create and return a new service asynchronously.
diff --git a/actix-service/src/transform.rs b/actix-service/src/transform.rs
index b0abe72b..8fdff66f 100644
--- a/actix-service/src/transform.rs
+++ b/actix-service/src/transform.rs
@@ -27,7 +27,7 @@ where
 /// Transform(middleware) wraps inner service and runs during inbound and/or outbound processing in
 /// the request/response lifecycle. It may modify request and/or response.
 ///
-/// For example, timeout transform:
+/// For example, a timeout service wrapper:
 ///
 /// ```ignore
 /// pub struct Timeout<S> {
@@ -35,11 +35,7 @@ where
 ///     timeout: Duration,
 /// }
 ///
-/// impl<S> Service for Timeout<S>
-/// where
-///     S: Service,
-/// {
-///     type Request = S::Request;
+/// impl<S: Service<Req>, Req> Service<Req> for Timeout<S> {
 ///     type Response = S::Response;
 ///     type Error = TimeoutError<S::Error>;
 ///     type Future = TimeoutServiceResponse<S>;
@@ -55,26 +51,22 @@ where
 /// }
 /// ```
 ///
-/// Timeout service in above example is decoupled from underlying service implementation and could
-/// be applied to any service.
+/// This wrapper service is decoupled from the underlying service implementation and could be
+/// applied to any service.
 ///
-/// The `Transform` trait defines the interface of a Service factory. `Transform` is often
+/// The `Transform` trait defines the interface of a service wrapper. `Transform` is often
 /// implemented for middleware, defining how to construct a middleware Service. A Service that is
 /// constructed by the factory takes the Service that follows it during execution as a parameter,
 /// assuming ownership of the next Service.
 ///
-/// Factory for `Timeout` middleware from the above example could look like this:
+/// A transform for the `Timeout` middleware could look like this:
 ///
 /// ```ignore
 /// pub struct TimeoutTransform {
 ///     timeout: Duration,
 /// }
 ///
-/// impl<S> Transform<S> for TimeoutTransform
-/// where
-///     S: Service,
-/// {
-///     type Request = S::Request;
+/// impl<S: Service<Req>, Req> Transform<S, Req> for TimeoutTransform {
 ///     type Response = S::Response;
 ///     type Error = TimeoutError<S::Error>;
 ///     type InitError = S::Error;
@@ -82,7 +74,7 @@ where
 ///     type Future = Ready<Result<Self::Transform, Self::InitError>>;
 ///
 ///     fn new_transform(&self, service: S) -> Self::Future {
-///         ready(Ok(TimeoutService {
+///         ready(Ok(Timeout {
 ///             service,
 ///             timeout: self.timeout,
 ///         }))
@@ -227,3 +219,54 @@ where
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use core::{
+        future::{ready, Ready},
+        time::Duration,
+    };
+
+    use super::*;
+    use crate::Service;
+
+    // pseudo-doctest for Transform trait
+    pub struct TimeoutTransform {
+        timeout: Duration,
+    }
+
+    // pseudo-doctest for Transform trait
+    impl<S: Service<Req>, Req> Transform<S, Req> for TimeoutTransform {
+        type Response = S::Response;
+        type Error = S::Error;
+        type InitError = S::Error;
+        type Transform = Timeout<S>;
+        type Future = Ready<Result<Self::Transform, Self::InitError>>;
+
+        fn new_transform(&self, service: S) -> Self::Future {
+            ready(Ok(Timeout {
+                service,
+                _timeout: self.timeout,
+            }))
+        }
+    }
+
+    // pseudo-doctest for Transform trait
+    pub struct Timeout<S> {
+        service: S,
+        _timeout: Duration,
+    }
+
+    // pseudo-doctest for Transform trait
+    impl<S: Service<Req>, Req> Service<Req> for Timeout<S> {
+        type Response = S::Response;
+        type Error = S::Error;
+        type Future = S::Future;
+
+        crate::forward_ready!(service);
+
+        fn call(&self, req: Req) -> Self::Future {
+            self.service.call(req)
+        }
+    }
+}