__DATA__
<sec id="00005"><no>1.1</no>
    <sec id="00010"><no>1.1.1</no>
    </sec>
    <sec id="00015"><no>1.1.2</no>
        <sec id="00020"><no>1.1.2.1</no>
        </sec>
        <sec id="00025"><no>1.1.2.2</no>
        </sec>
    </sec>
    <sec id="00015"><no>1.1.3</no>
    </sec>
</sec>
<sec id="00005"><no>1.2</no>
    <sec id="00010"><no>1.2.1</no>
    </sec>
    <sec id="00015"><no>1.2.2</no>
        </sec>
        <sec id="00020"><no>1.2.2.1</no>
        </sec>
        <sec id="00025"><no>1.2.2.2</no>
    </sec>
    <sec id="00015"><no>1.2.3</no>
    </sec>
</sec>

Section nesting error in or before 1.2.2.1
Section nesting error in or before 1.2.2.2
Section nesting error in or before 1.2.3