# Define base variable detector: any (possibly-nested) angle-bracketed string.
# Patterns to extract <variables> or >variables< from a string.
my $out_angled;
$out_angled = qr/ < ( [^<>] | (??{$out_angled}) )* > /x;
                  # open angle-bracket then ...
                      # non-angle chars ...
                            # or ...
                               # another angle-bracketed item ...
                                                 # if there are any ...
                                                   # and a close angle-bracket