define UTF8CONT [
"80"|"81"|"82"|"83"|"84"|"85"|"86"|"87"|"88"|"89"|"8A"|"8B"|"8C"|"8D"|"8E"|"8F"|
"90"|"91"|"92"|"93"|"94"|"95"|"96"|"97"|"98"|"99"|"9A"|"9B"|"9C"|"9D"|"9E"|"9F"|
"A0"|"A1"|"A2"|"A3"|"A4"|"A5"|"A6"|"A7"|"A8"|"A9"|"AA"|"AB"|"AC"|"AD"|"AE"|"AF"|
"B0"|"B1"|"B2"|"B3"|"B4"|"B5"|"B6"|"B7"|"B8"|"B9"|"BA"|"BB"|"BC"|"BD"|"BE"|"BF"
];

define UTF8'2'BYTE [
"C0"|"C1"|"C2"|"C3"|"C4"|"C5"|"C6"|"C7"|"C8"|"C9"|"CA"|"CB"|"CC"|"CD"|"CE"|"CF"|
"D0"|"D1"|"D2"|"D3"|"D4"|"D5"|"D6"|"D7"|"D8"|"D9"|"DA"|"DB"|"DC"|"DD"|"DE"|"DF"
];
define UTF8'3'BYTE [
"E0"|"E1"|"E2"|"E3"|"E4"|"E5"|"E6"|"E7"|"E8"|"E9"|"EA"|"EB"|"EC"|"ED"|"EE"|"EF"
];
define UTF8'4'BYTE [
"F0"|"F1"|"F2"|"F3"|"F4"|"F5"|"F6"|"F7"
];
define UTF8'INVALID [
"F8"|"F9"|"FA"|"FB"|"FC"|"FD"|"FE"|"FF"
];
# define the largest class, the 1 byte characters, by negation so they end
# up being handled by the "anything else" case in foma.
define UTF8'1'BYTE \[
  UTF8'2'BYTE | UTF8'3'BYTE | UTF8'4'BYTE | UTF8'INVALID | UTF8CONT
];

define VALID'UTF8 [
  [ UTF8'1'BYTE ] |
  [ UTF8'2'BYTE UTF8CONT ] |
  [ UTF8'3'BYTE UTF8CONT UTF8CONT ] |
  [ UTF8'4'BYTE UTF8CONT UTF8CONT UTF8CONT ]
]*;