GUACAMOLE-1293: Correct and add missing comments for accuracy and clarity.

guacamole-common-js/src/main/webapp/modules/Client.js

@@ -1856,7 +1856,7 @@ Guacamole.Client.Message = {
     
     /**
      * A client message that indicates that a user has joined an existing
-     * connection. This message xpects a single additional argument - the
+     * connection. This message expects a single additional argument - the
      * username of the user who has joined the connection.
      * 
      * @type {!number}

guacamole/src/main/frontend/src/app/client/directives/guacClientMessage.js

@@ -41,6 +41,7 @@ angular.module('client').directive('guacClientMessage', [function guacClientMess
         controller: ['$scope', '$injector', '$element',
                 function guacClientMessageController($scope, $injector, $element) {
             
+            // Required types
             const ManagedClientMessage = $injector.get('ManagedClientMessage');
             
             /**
@@ -61,7 +62,9 @@ angular.module('client').directive('guacClientMessage', [function guacClientMess
             /**
              * Returns a set of key/value object pairs that represent the
              * arguments provided as part of the message in the form
-             * ARGS[0] = value.
+             * ARGS[0] = value. Guacamole's translation system relies on
+             * the arguments being available in this format in order to be able
+             * to handle substituting values for an arbitrary list of arguments.
              * 
              * @returns {Object}
              */