docs: private AbstractRule processConstraint(RulesTextProvider textProvider)
      	throws ParserException
      {
      	log.debug("processConstraint");
          Constraint rule = new Constraint();
          int start = textProvider.getPos();
          LoadCommonRuleData(rule,textProvider);
          textProvider.addTOCElement(null, rule.getDescription(), start, textProvider.getPos(), TYPE_CONSTRAINT);
          exactOrError("{",textProvider);
          Expression condition = processAction(textProvider);
          if (condition.isAssign())
          {
              throw new ParserException("Found an assignment in a condition ",textProvider);
          }
          exactOrError("}",textProvider);
          rule.addCondition(condition);
  
          return rule;
      }