docs: def _get_regular_expression_of_symbols(self):
          """
          Returns the regular expression to search all symbols.
  
          :return: The regular expression to search all symbols.
          :rtype: str
          """
  
          regular_expression = None
          for symbol in self.symbols:
              formated_symbol = self._get_formated_symbol(symbol['symbol'])
              if regular_expression is None:
                  regular_expression = '(' + formated_symbol + ')'
              else:
                  regular_expression = (
                      regular_expression +
                      '|(' +
                      formated_symbol +
                      ')'
                  )
          return regular_expression