+# check that a field only has callsign characters in it but has more than the standard 3 callsign letters
+sub is_long_callsign
+{
+ 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]{1,5} # 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;
+}
+
+sub is_prefix
+{
+ return $_[0] =~ m!^(?:[A-Z]{1,2}\d+ | \d[A-Z]{1,2}\d+)!x # basic prefix
+}
+
+