{
return $_[0] =~ m!^(?:[A-Z]{1,2}\d+ | \d[A-Z]{1,2}\d+) # basic prefix
(?:/(?:[A-Z]{1,2}\d+ | \d[A-Z]{1,2}\d+))? # / another one (possibly)
- [A-Z]{1,3} # callsign letters
+ [A-Z]{1,4} # callsign letters
(?:/(?:[A-Z]{1,2}\d+ | \d[A-Z]{1,2}\d+))? # / another prefix possibly
(?:/[0-9A-Z]{1,2})? # /0-9A-Z+ possibly
(?:-\d{1,2})? # - nn possibly