code: public static Rule getRule(final String inequalitySymbol,
                               final String field,
                               final String value) {
      if (field.equalsIgnoreCase(LoggingEventFieldResolver.LEVEL_FIELD)) {
        //push the value back on the stack and
          // allow the level-specific rule pop values
        return LevelInequalityRule.getRule(inequalitySymbol, value);
      } else if (
              field.equalsIgnoreCase(LoggingEventFieldResolver.TIMESTAMP_FIELD)) {
        return TimestampInequalityRule.getRule(inequalitySymbol, value);
      } else {
        return new InequalityRule(inequalitySymbol, field, value);
      }
    }
docs: Create new instance from top two elements on stack.
  @param inequalitySymbol inequality symbol.
  @param field field.
  @param value comparison value.
  @return rule.