Class Definitions

Class upper

Includes characters that can be classified as uppercase letters.
The uppercase letters <A> to <Z>, as defined by every character set are automatically included in this class.
No character specified for the keywords digit, punct, cntrl or space shall be specified.

Example:
In the POSIX locale, the 26 uppercase letters shall be included:

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

Class lower

Includes characters that can be classified as lowercase letters.
The lowercase letters <a> to <z>, as defined by every character set are automatically included in this class.
No character specified for the keywords cntrl, digit, punct, or space shall be specified.

Example:
In the POSIX locale, the 26 lowercase letters shall be included:

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

Class alpha

Includes characters that can be classified as letters/alphabets.

No character specified for the keywords cntrl, digit, punct, or space shall be specified.
Characters classified as either upper or lower are automatically included in this class.

Example:
In the POSIX locale, all characters in the classes upper and lower shall be included.

Class digit

Includes characters that can be classified as numeric digits. Only the digits <zero>, <one>, <two>, <three>, <four>, <five>, <six>, <seven>, <eight>, and <nine> shall be specified, and in contiguous ascending sequence by numerical value. The digits <zero> to <nine> of every character set are automatically included in this class.

Example:
In the POSIX locale, only:

0 1 2 3 4 5 6 7 8 9

shall be included.

Class alnum

Includes characters that can be classified as letters and digits(characters used to represent numeric value). Only the characters specified for the class alpha and class digit shall be specified.

Class space

Includes characters that can be classified as white-space characters.
No character specified for the keywords upper, lower, alpha, digit, graph, or xdigit shall be specified.
Any characters included in the class blank and the <newline>, <carriage-return>, <space>, <form-feed>, <tab>, and <vertical-tab> of the every character set are automatically included in this class.

Example:
In the POSIX locale, at a minimum, the <space>, <form-feed>, <newline>, <carriage-return>, <tab>, and <vertical-tab> shall be included.

Class blank

Includes characters that can be classified as <blank>s. The <space> and <tab> are automatically included in this class.

Example:
In the POSIX locale, only the <space> and <tab> shall be included.

Class cntrl

Includes characters that can be classified as control characters.
No character specified for the keywords upper, lower, alpha, digit, punct, graph, print, or xdigit shall be specified.

Example:
In the POSIX locale, no characters in classes alpha or print shall be included.

Class punct

Includes characters that can be classified as punctuation characters.
No character specified for the keywords upper, lower, alpha, digit, cntrl, xdigit, or as the <space> shall be specified.

Example:
In the POSIX locale, neither the <space> nor any characters in classes alpha, digit, or cntrl shall be included.

Class graph

Includes characters that can be classified as printable characters, not including the <space>. Characters specified for the keywords upper, lower, alpha, digit, xdigit, and punct are automatically included in this class. No character specified for the keyword cntrl shall be specified.

Example:
In the POSIX locale, all characters in classes alpha, digit, and punct shall be included; no characters in class cntrl shall be included.

Class print

Includes characters that can be classified as printable characters, including the <space>. Characters specified for the keywords upper, lower, alpha, digit, xdigit, punct, graph, and the <space> are automatically included in this class. No character specified for the keyword cntrl shall be specified.

Example:
In the POSIX locale, all characters in class graph shall be included; no characters in class cntrl shall be included.

Class toupper

Defines the mapping of lowercase letters to uppercase letters, within that character set.

Example:
In the POSIX locale, at a minimum, the 26 lowercase 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

shall be mapped to the corresponding 26 uppercase 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

Class tolower

Defines the mapping of uppercase letters to lowercase letters, within that character set.

In the POSIX locale, at a minimum, the 26 uppercase characters:

Example:
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

shall be mapped to the corresponding 26 lowercase 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

Class xdigit

Includes characters that can be classified as hexadecimal digits.

Only the characters defined for the class digit shall be specified, in contiguous ascending sequence by numerical value, followed by one or more sets of six characters representing the hexadecimal digits 10 to 15 inclusive, with each set in ascending order (for example, <A>, <B>, <C>, <D>, <E>, <F>, <a>, <b>, <c>, <d>, <e>, <f>). The digits <zero> to <nine>, the uppercase letters <A> to <F>, and the lowercase letters <a> to <f> of the portable character set are automatically included in this class.

Example:
In the POSIX locale, only:

0 1 2 3 4 5 6 7 8 9 A B C D E F a b c d e f

shall be included.

Notes

Each of these classes include the respective characters as mentioned above, from all the locales supported. This means each class is a pool of characters belonging to the mentioned category, from various locales supported.