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