$txt =~ s{(?<=[\w&;\\\-:\/])$nl\s*$nl(?=\s*[\w&;\\\-:\/])}{</p><p>}g 
        if ( defined $nl );
$txt =~ s{(?<=[\w&;\\\-:\/])$nl(?=\s*[\w&;\\\-:\/])}{</p><p>}g    
        if ( defined $nl );