code: def add_alternative (self, target):
          
          assert isinstance(target, BasicTarget)
          d = target.default_build ()
  
          if self.alternatives_ and self.default_build_ != d:
              get_manager().errors()("default build must be identical in all alternatives\n"
                "main target is '%s'\n"
                "with '%s'\n"
                "differing from previous default build: '%s'" % (self.full_name (), d.raw (), self.default_build_.raw ()))
  
          else:
              self.default_build_ = d
  
          self.alternatives_.append (target)
docs: Add a new alternative for this target.