(?(?{NOT-COND})(?!))

##</code><code>##

(?(?{COND})|(?!))

##</code><code>##

/\b(\d+)\b(?(?{not($1 >= 128 && $1 <= 255)})(?!))/

##</code><code>##

/\b(\d+)\b(?(?{$1 >= 128 && $1 <= 255})|(?!))/