+# check that a field only has callsign characters in it
+sub is_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]{1,4} # 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
+ $!x;
+}
+
+# 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
+}
+
+
+# check that a PC protocol field is valid text
+sub is_pctext
+{
+ return undef unless length $_[0];
+ return undef if $_[0] =~ /[\x00-\x08\x0a-\x1f\x80-\x9f]/;
+ return 1;
+}
+
+# check that a PC prot flag is fairly valid (doesn't check the difference between 1/0 and */-)
+sub is_pcflag
+{
+ return $_[0] =~ /^[01\*\-]+$/;
+}
+
+# check that a thing is a frequency
+sub is_freq
+{
+ return $_[0] =~ /^\d+(?:\.\d+)?$/;
+}
+
+# check that a thing is just digits
+sub is_digits
+{
+ return $_[0] =~ /^[\d]+$/;
+}
+
+# does it look like a qra locator?
+sub is_qra
+{
+ return $_[0] =~ /^[A-Ra-r][A-Ra-r]\d\d[A-Xa-x][A-Xa-x]$/;
+}
+
+# does it look like a valid lat/long
+sub is_latlong
+{
+ return $_[0] =~ /^\s*\d{1,2}\s+\d{1,2}\s*[NnSs]\s+1?\d{1,2}\s+\d{1,2}\s*[EeWw]\s*$/;
+}