Update MessageCatcher docs to clarify usage (#5870)

editions/tw5.com/tiddlers/widgets/MessageCatcherWidget.tid

@@ -1,5 +1,5 @@
 created: 20210309133636211
-modified: 20210309133636211
+modified: 20210711193113104
 tags: Widgets
 title: MessageCatcherWidget
 type: text/vnd.tiddlywiki
@@ -15,9 +15,9 @@ The message catcher widget traps [[messages|Messages]] dispatched within its chi
 The content of the `<$messagecatcher>` widget is displayed normally.
 
 |!Attribute |!Description |
-|type |Name of the message be trapped, for example "tm-scroll" or "tm-navigate" |
-|actions |Action string to be invoked when a matching message is trapped |
-|//{any attributes starting with $}// |Each attribute name (excluding the $) specifies the name of a message, and the value specifies the action string to be invoked  |
+|//{any attributes starting with $}// |Each attribute name (excluding the $) specifies the name of a message, and the value specifies the action string to be invoked |
+|type |Name of the message be trapped, for example "tm-scroll" or "tm-navigate". The `type` and `actions` attributes can be useful when the type of event needs to be specified via a variable or text reference |
+|actions |Action string to be invoked when a matching message is trapped. Must be used in conjunction with the `type` attribute |
 
 ! Variables
 
@@ -41,3 +41,4 @@ Click on [[this link]] to fire an action. See the browser JavaScript console for
 
 </$messagecatcher>
 """/>
+