<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def register(self, id):
 """ Registers a configuration. Returns True if the configuration has been added and False if it already exists. Reports an error if the configuration is 'used'. """

        assert isinstance(id, basestring)
        if id in self.used_:
            #FIXME
            errors.error("common: the configuration '$(id)' is in use")

        if id not in self.all_:
            self.all_.add(id)

            # Indicate that a new configuration has been added.
            return True
        else:
            return False