diff --git a/README.md b/README.md
index 6ea6422..273db3c 100644
--- a/README.md
+++ b/README.md
@@ -2,6 +2,8 @@
 
 Package errors provides simple error handling primitives.
 
+`go get github.com/pkg/errors`
+
 The traditional error handling idiom in Go is roughly akin to
 ```go
 if err != nil {
diff --git a/errors.go b/errors.go
index 6c45c8d..71f1431 100644
--- a/errors.go
+++ b/errors.go
@@ -28,7 +28,7 @@
 // to reverse the operation of errors.Wrap to retrieve the original error
 // for inspection. Any error value which implements this interface
 //
-//     type Causer interface {
+//     type causer interface {
 //             Cause() error
 //     }
 //
@@ -43,6 +43,9 @@
 //             // unknown error
 //     }
 //
+// causer interface is not exported by this package, but is considered a part
+// of stable public API.
+//
 // Formatted printing of errors
 //
 // All error values returned from this package implement fmt.Formatter and can
@@ -77,6 +80,9 @@
 //             }
 //     }
 //
+// stackTracer interface is not exported by this package, but is considered a part
+// of stable public API.
+//
 // See the documentation for Frame.Format for more details.
 package errors
 
@@ -191,7 +197,7 @@ func Wrapf(err error, format string, args ...interface{}) error {
 // An error value has a cause if it implements the following
 // interface:
 //
-//     type Causer interface {
+//     type causer interface {
 //            Cause() error
 //     }
 //