+# check that a field only has callsign characters in it
+sub is_callsign
+{
+ return $_[0] =~ m!^
+ (?:\d?[A-Z]{1,2}\d*/)? # out of area prefix /
+ (?:\d?[A-Z]{1,2}\d+) # main prefix one (required)
+ [A-Z]{1,5} # callsign letters (required)
+ (?:-(?:\d{1,2}|\#))? # - nn possibly (eg G8BPQ-8) or -# (an RBN spot)
+ (?:/[0-9A-Z]{1,7})? # / another prefix, callsign or special label (including /MM, /P as well as /EURO or /LGT) possibly
+ $!x;
+
+ # longest callign allowed is 1X11/1Y11XXXXX-11/XXXXXXX
+}
+
+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 unless length $_[0] == 4 || length $_[0] == 6;
+ 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 $_[0] =~ /^\s*\d{1,2}\s+\d{1,2}\s*[NnSs]\s+1?\d{1,2}\s+\d{1,2}\s*[EeWw]\s*$/;
+}
+
+# is it an ip address?
+sub is_ipaddr
+{
+ return $_[0] =~ /^\d+\.\d+\.\d+\.\d+$/ || $_[0] =~ /^[0-9a-f:,]+$/;
+}
+
+# insert an item into a list if it isn't already there returns 1 if there 0 if not
+sub insertitem
+{
+ my $list = shift;
+ my $item = shift;
+
+ return 1 if grep {$_ eq $item } @$list;
+ push @$list, $item;
+ return 0;
+}