def register(self, name, function, plugin, description=None):
        """
        Registers a new document.

        .. warning: You can not use any relative links inside a given document.
                    For instance, sphinx's toctree, image, figure or include statements do not work.

        :param function: Function, which gets called for the new thread
        :type function: function
        :param name: Unique name of the thread for documentation purposes.
        :param plugin: Plugin object, under which the threads where registered
        :type plugin: GwBasePattern
        :param description: Short description of the thread
        """
        if name in self.threads.keys():
            raise ThreadExistsException("Thread %s was already registered by %s" %
                                        (name, self.threads[name].plugin.name))

        self.threads[name] = Thread(name, function, plugin, description)
        self.__log.debug("Thread %s registered by %s" % (name, plugin.name))
        return self.threads[name]