http://www.perlmonks.org?node_id=424166


in reply to Things you think you'll never use.

Why not something like this: 

$re = qr{
   \<
   (?:
      (?> [^<>]+ )    # Non-parens without backtracking
    |
      (??{ $re })     # Group with matching parens
   )*
   \>
}x;

$s = "B<I<U<bold underlined text>>> and B<bold text>";

1 while $s =~ s{([BUI])<([^<>]*(?:$re[^<>]*)*)>}{<$1>$2</$1>}g;

print $s,"\n";

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Jenda
We'd like to help you learn to help yourself
Look around you, all you see are sympathetic eyes
Stroll around the grounds until you feel at home
   -- P. Simon in Mrs. Robinson

In Section Meditations