Document that default ping handler can block

doc.go

@@ -85,18 +85,22 @@
 // and pong. Call the connection WriteControl, WriteMessage or NextWriter
 // methods to send a control message to the peer.
 //
-// Connections handle received ping and pong messages by invoking callback
-// functions set with SetPingHandler and SetPongHandler methods. The default
-// ping handler sends a pong to the client. The callback functions can be
-// invoked from the NextReader, ReadMessage or the message Read method.
-//
 // Connections handle received close messages by sending a close message to the
 // peer and returning a *CloseError from the the NextReader, ReadMessage or the
 // message Read method.
 //
-// The application must read the connection to process ping and close messages
-// sent from the peer. If the application is not otherwise interested in
-// messages from the peer, then the application should start a goroutine to
+// Connections handle received ping and pong messages by invoking callback
+// functions set with SetPingHandler and SetPongHandler methods. The callback
+// functions are called from the NextReader, ReadMessage and the message Read
+// methods.
+//
+// The default ping handler sends a pong to the peer. The application's reading
+// goroutine can block for a short time while the handler writes the pong data
+// to the connection.
+//
+// The application must read the connection to process ping, pong and close
+// messages sent from the peer. If the application is not otherwise interested
+// in messages from the peer, then the application should start a goroutine to
 // read and discard messages from the peer. A simple example is:
 //
 //  func readLoop(c *websocket.Conn) {