While it's true that it's not generally a good idea to try to parse html with regexen, "(t)hat simply can't work is not.

It can be done... and often is for simple cases... but is fraught with so many difficulties that it's inadvisable. What's more, trying to parse html of any complexity with tools other than the well-tested modules referenced above flies in the face of the mantra 'don't re-invent the wheel.'

from perlfaq6

Here's code that finds everything between START and END in a paragraph:

undef $/; # read in whole file, not just one line or paragraph
while ( <> ) {
  while ( /START(.*?)END/sgm ) {
    print "$1\n";
    }
}
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