open :F html input.html ;
for my $h2 in //h2 {
    my $h1 = $h2/following-sibling::h1[1] ;
    my $chunk ;
    if $h1 {
        $chunk = $h2/following-sibling::text()[following-sibling::h1[1
+]=$h1][preceding-sibling::h2[1]=$h2]
               | $h2/following-sibling::*[not(self::h2)][following-sib
+ling::h1[1]=$h1][preceding-sibling::h2[1]=$h2] ;
    } else {
        $chunk = $h2/following-sibling::text()[preceding-sibling::h2[1
+]=$h2]
               | $h2/following-sibling::*[not(self::h2)][preceding-sib
+ling::h2[1]=$h2] ;
    }
    if $chunk {
        my $div := insert element div after $h2 ;
        xmove $chunk into $div ;
    }
}
my $divs := wrap div //h2 ;
save :F html :f output.html ;
[download]

<h1>blah</h1>
<p>blah</p>
<p>

</p>
<div><h2>blah</h2></div>
<div>
<p>blah</p>
<h3>blah</h3>
<p>blah</p>

</div>
<div><h2>blah blah blah</h2></div>
<div>
<p>blah</p>

</div>
<h1>blah</h1>
<div><h2>blah</h2></div>
<div>


</div>
<div><h2>blah</h2></div>
</body></html>
[download]

($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,
[download]