Das sind mal praktische Teile…

 [[:alnum:]]  - [A-Za-z0-9]     Alphanumeric characters
 [[:alpha:]]  - [A-Za-z]        Alphabetic characters
 [[:blank:]]  - [ \x09]         Space or tab characters only
 [[:cntrl:]]  - [\x00-\x19\x7F] Control characters
 [[:digit:]]  - [0-9]           Numeric characters
 [[:graph:]]  - [!-~]           Printable and visible characters
 [[:lower:]]  - [a-z]           Lower-case alphabetic characters
 [[:print:]]  - [ -~]           Printable (non-Control) characters
 [[:punct:]]  - [!-/:-@[-`{-~]  Punctuation characters
 [[:space:]]  - [ \t\v\f]       All whitespace chars
 [[:upper:]]  - [A-Z]           Upper-case alphabetic characters
 [[:xdigit:]] - [0-9a-fA-F]     Hexadecimal digit characters

Note that [[:graph:]] does not match the space ” “, but [[:print:]] does. Some character classes may (or may not) match characters in the high ASCII range (ASCII 128-255 or 0x80-0xFF), depending on which C library was used to compile sed. For non-English languages, [[:alpha:]] and other classes may also match high ASCII characters.

Aus der sehr, sehr lesenswerten (wenn man denn so was interessant findet) sed FAQ von Eric Pement.