The definition of character class digit requires that only ten characters
-the ones defining digits- can be specified; alternate digits (for
example, Hindi or Kanji) cannot be specified here. However, the encoding
may vary if an implementation supports more than one encoding.
The definition of character class xdigit requires that the characters
included in character class digit are included here also and allows for
different symbols for the hexadecimal digits 10 through 15.
