Messages can be posted from the host app to this using the
functions ::PostWebMessageAsJson and
::PostWebMessageAsString. Try using the menu item
"Script->" to send the message {"SetColor":"blue"}.
It should change the text color of this paragraph.
The host app can receive messages by registering an event handler with
::HandleWebMessage. If you enter text and click
"Send", this will send a message to the host app which will change the text of
the title bar.
The host app can send messages back in response to received messages. If you click "Get window bounds", the host app will report back the bounds of its window, which will appear in the text box.