def addErrback(self, errback, *args, **kw):
        """
        Add a failure callback that will be run in the context of an eliot
        action.

        @return: C{self}
        @rtype: L{DeferredContext}

        @raises AlreadyFinished: L{DeferredContext.addActionFinish} has been
            called. This indicates a programmer error.
        """
        return self.addCallbacks(
            _passthrough, errback, errbackArgs=args, errbackKeywords=kw)
Add a failure callback that will be run in the context of an eliot
        action.

        @return: C{self}
        @rtype: L{DeferredContext}

        @raises AlreadyFinished: L{DeferredContext.addActionFinish} has been
            called. This indicates a programmer error.