docs: def visit_oper(self, node, _):
          """Return an operator as a string. Currently only "=" and ":" (both synonyms)
  
          Arguments
          ---------
          node : parsimonious.nodes.Node.
          _ (children) : list, unused
  
          Result
          ------
          str
              The operator as a string.
  
          Example
          -------
  
          >>> BaseParser('=', default_rule='OPER').data
          '='
          >>> BaseParser(':', default_rule='OPER').data
          '='
  
          """
  
          oper = node.text
          if oper == ':':
              oper = '='
          return oper