section nesting

[anniyan]

I am new to perl. I am doing a validation tool to check the section nesting. If no proper nesting, error should be thrown. Yesterday i posted the same question asked assistance with twig coding. Is it possible to find the proper section nesting without using XML::Twig? If so please assist me.

$q ='<sec id="00005"><no>1.1</no>
sfasfasdfadsfsdaf
    <sec id="00010"><no>1.1.1</no>
    sahfjsahdfasddfj
    </sec
    <sec id="00015"><no>1.1.2</no>
    sahfjsahdfasddfj
        <sec id="00020"><no>1.1.2.1</no>
        sahfjsahdfasddfj
        </sec>
        <sec id="00025"><no>1.1.2.2</no>
        safksajdklfasd
        </sec>
    </sec>
    <sec id="00015"><no>1.1.3</no>
    sahfjsahdfasddfj
    </sec>
</sec>
<sec id="00005"><no>1.2</no>
sfasfasdfadsfsdaf
........';