The alphabetic characters are a subset of the graphic characters. Of the standard characters, only these are the alphabetic characters:
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
a b c d e f g h i j k l m n o p q r s t u v w x y z
Any implementation-defined character that has case must be alphabetic. For each implementation-defined graphic character that has no case, it is implementation-defined whether that character is alphabetic.