HTML Widgets and Portals; Response from widget.GetString always has a MIME type of "text/plain"

The HTTP header returned from any HTML Widget event called via widget.GetString JavaScript command always specifies a MIME type of "text/plain".

This is by design since we do not dictate the format of the data returned from a widget event. It may well be a simple text message or maybe a piece of HTML to be viewed in a widget.UI.PreviewPane control. It just so happens that most of our responses tend to be JSON text.

Therefore we don't specify a MIME type of "application/json".

Also, to keep things simple for HTML Widget development, we do not require (or even give the ability for) a developer to specify the format of the data they are returning.