code: def as_symbols(self):
          
          out = set()
          for name in self.types:
              out.add(('type', name))
          for name in self.enums:
              out.add(('enum', name))
          for name in self.commands:
              out.add(('command', name))
          return out
docs: Set of symbols required by this Require
  
          :return: set of ``(symbol type, symbol name)`` tuples