diff --git a/metadata/metadata.go b/metadata/metadata.go
index 65dc5af5..73323950 100644
--- a/metadata/metadata.go
+++ b/metadata/metadata.go
@@ -32,6 +32,7 @@
  */
 
 // Package metadata define the structure of the metadata supported by gRPC library.
+// Please refer to http://www.grpc.io/docs/guides/wire.html for more information about custom-metadata.
 package metadata // import "google.golang.org/grpc/metadata"
 
 import (
@@ -82,6 +83,7 @@ func DecodeKeyValue(k, v string) (string, string, error) {
 type MD map[string][]string
 
 // New creates a MD from given key-value map.
+// Keys are automatically converted to lowercase. And for keys having "-bin" as suffix, their values will be applied Base64 encoding.
 func New(m map[string]string) MD {
 	md := MD{}
 	for k, v := range m {
@@ -93,6 +95,7 @@ func New(m map[string]string) MD {
 
 // Pairs returns an MD formed by the mapping of key, value ...
 // Pairs panics if len(kv) is odd.
+// Keys are automatically converted to lowercase. And for keys having "-bin" as suffix, their values will be appplied Base64 encoding.
 func Pairs(kv ...string) MD {
 	if len(kv)%2 == 1 {
 		panic(fmt.Sprintf("metadata: Pairs got the odd number of input pairs for metadata: %d", len(kv)))
diff --git a/rpc_util.go b/rpc_util.go
index da88dad4..d98a8837 100644
--- a/rpc_util.go
+++ b/rpc_util.go
@@ -198,7 +198,7 @@ func Peer(peer *peer.Peer) CallOption {
 // immediately. Otherwise, the RPC client will block the call until a
 // connection is available (or the call is canceled or times out) and will retry
 // the call if it fails due to a transient error. Please refer to
-// https://github.com/grpc/grpc/blob/master/doc/fail_fast.md
+// https://github.com/grpc/grpc/blob/master/doc/fail_fast.md. Note: failFast is default to true.
 func FailFast(failFast bool) CallOption {
 	return beforeCall(func(c *callInfo) error {
 		c.failFast = failFast