There is no plugin for Cappuccino (since Xcode 4 does not allow plugins).
If you are talking about XCodeCapp, this is actually a separate application that you run. You can learn more about how it works here: http://antoinemercadal.fr/xcodecappcocoa/
There was a long-standing plugin a long time ago, but it has been deprecated a long time ago and, of course, will no longer work with Xcode, as version 4 no longer allows plug-ins.
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