docs: private AbstractRule processFormula(RulesTextProvider textProvider)
      {
      	log.debug("processFormula");
          Formula rule = new Formula();
          int start = textProvider.getPos();
          LoadCommonRuleData(rule,textProvider);
          textProvider.addTOCElement(null, rule.getDescription(), start, textProvider.getPos(), TYPE_FORMULA);
          exactOrError("{",textProvider);
          Expression expression = processAction(textProvider);
          exactOrError("}",textProvider);
          rule.addAction(expression);
  
          return rule;
      }