Last modified: 2012-04-16 09:16:05 UTC
Right now when display of a special page is blocked due to it being in a frame and $wgEditPageFrameOptions being set to DENY or SAMEORIGIN, nothing is output at all. This gives developers the impression that something is broken rather than hidden on purpose. It would be nice if an error message were displayed in these cases. Something like "This page cannot be displayed within a frame." or something similar.
X-Frame-Options is an instruction to the browser. There is no interface that lets a server understand if a page is being loaded in a frame, only an instruction to tell a browser to not load a page in an iframe even though it's loaded everything. The browser is the only one capable of displaying a warning like that. This isn't a bug in MediaWiki because it is the browser that is displaying the frame as blank like that and we have no control over it.