private static MarkupSelectorItem.AttributeCondition.Operator parseAttributeOperator(final String operatorStr) {
        if (operatorStr == null) {
            return null;
        }
        if ("=".equals(operatorStr)) {
            return MarkupSelectorItem.AttributeCondition.Operator.EQUALS;
        }
        if ("!=".equals(operatorStr)) {
            return MarkupSelectorItem.AttributeCondition.Operator.NOT_EQUALS;
        }
        if ("^=".equals(operatorStr)) {
            return MarkupSelectorItem.AttributeCondition.Operator.STARTS_WITH;
        }
        if ("$=".equals(operatorStr)) {
            return MarkupSelectorItem.AttributeCondition.Operator.ENDS_WITH;
        }
        if ("*=".equals(operatorStr)) {
            return MarkupSelectorItem.AttributeCondition.Operator.CONTAINS;
        }
        if ("!".equals(operatorStr)) {
            return MarkupSelectorItem.AttributeCondition.Operator.NOT_EXISTS;
        }
        if ("".equals(operatorStr)) {
            return MarkupSelectorItem.AttributeCondition.Operator.EXISTS;
        }
        return null;
    }