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To display images and other files from the filesystem in the editor, the BaseHref must be set (see above example).
Because BaseHref cannot include parameters, I have set the BaseHref to just the baseWorkerURL. The browser will append the relative URL filenames to this URL. The appended URL will then be sent to the channel. To capture this request, I have made the Channel privileged and inspect the URL in setPortalControlStructures. If BaseWorker is called with no query parameters, I strip off the filename and set the downloadfile field in ThemeState. When ThemeState.setNextState is subsequently called, I set up a DownloadWorker for the requested file.
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