What is the problem with this regex?

Question

First, I'm not a regex expert, so I'm pretty sure I'm doing something wrong.

Here is my regular expression:

<(list)(\b[^>]*)>(<\1\b[^>]*>.*?<\/\1>|.)*?<\/\1>

This is the input string:

...
<list title="Lorem ipsum dolor sit amet, consectetur adipiscing elit...">
<li>
    <list title="Lorem adipiscing...">
        <li>Lorem ipsum dolor sit amet, consectetur adipiscing elit</li>
        <li>Lorem ipsum dolor sit amet, consectetur adipiscing elit</li>
    </list>
</li>
<li>
     <list title="Lorem ipsum...">
        <li>Lorem ipsum dolor sit amet, consectetur adipiscing elit</li>
    </list>
</li>
<li>Lorem ipsum dolor sit amet, consectetur adipiscing elit
</li>
<li>Lorem ipsum dolor sit amet, consectetur adipiscing elit
</li>
</list>
...

I want to match the external <list> and catch all the content including the intertal <list> but when I try to read the group \3 is empty althoug groups \1 and \2 are fine.

Any ideas would be very much appreciated.

Answer 1

This problem cannot be solved with a regular expression match. Seriously. I'm not just repeating the "don't parse HTML with regex" dogma; regular expressions are logically incapable of handling nested tags (which is why everyone says "don't parse HTML with regex")

The best idea I can give you is to use an XML parser. If you insist on solving this problem using regular expressions, you will wind up writing your own recursive-descent parser anyway, so you might as well take advantage of the work others have done on that problem already.