I’ve submitted a patch (Attachment #77777 and a couple of screenshots ( Attachment #77774 y Attachment #77776) to Bug #201116. It’s only a preliminary work but it enables the user to select with contentMergeViewer to use with each FileType/ContentType. Now it’s only useful if you use my java formatting compare plugin. Currently the org.eclipse.compare subsystem will allow only one contentMergeViewer per fileType or contentType and you cannot tell which one it will be as Szymon Brandys comments. With this patch the user can select/switch which one he wants to use among all viewer registered for a given file extension/content type.