Note It is not recommended to change the class of the special characters, since in some cases it might make it impossible to correctly parse Prolog terms.
The following table lists the character classes and the default corresponding characters:
 Class          Default member characters
---------------------------------------------------------
 upper_case     all upper case letters
 underline      _
 lower_case     all lower case letters
 digit          digits
 blank_space    space, tab and nonprintable characters
 end_of_line    newline (NL)
 atom_quote     '
 string_quote   "
 list_quote
 radix
 ascii
 solo           ! ;
 special        ( [ { ) ] } , |
 line_comment   %
 escape         \
 first_comment  /
 second_comment *
 symbol         # + - . : < = > ? @ ^ ` ~ & $
 terminator
Success:
   % The following example illustrates the use
   % of set_chtab/2 to redefine the class of the
   % dollar symbol.
   %
   [eclipse]: X = $a.
                 ^ (here?)
   syntax error: postfix/infix operator expected
   [eclipse]: set_chtab(0'$, lower_case).
   yes.
   [eclipse]: X = $a.
   X = $a
   yes.
   [eclipse]:
Error:
   set_chtab("a",symbol).       (Error 5)
   set_chtab(97,fred).          (Error 6)