'''string is''' ''class ?'''''-strict'''''? ?'''''-failindex''' ''varname? string''

Returns '''1''' if ''string'' is a valid member of the specified character class, otherwise returns '''0'''. If '''-strict''' is specified, then an empty string returns '''0''', otherwise an empty string will return '''1''' on any class. 
If '''-failindex''' is specified, then if the function returns '''0''', the index in the string where the class was no longer valid will be stored in the variable named ''varname''. 
The ''varname'' will not be set if the function returns '''1'''. 
The following character classes are recognized (the class name can be abbreviated):

   alnum:   Any Unicode alphabet or digit character.

   alpha:   Any Unicode alphabet character.

   ascii:   Any character with a value less than \u0080 (those that are in the 7-bit ascii range).

   boolean:   Any of the forms allowed to Tcl_GetBoolean.

   control:   Any Unicode control character.

   digit:   Any Unicode digit character. Note that this includes characters outside of the [[0-9]] range.

   double:   Any of the valid forms for a double in Tcl, with optional surrounding whitespace. In case of under/overflow in the value, 0 is returned and the varname will contain -1.

   false:   Any of the forms allowed to Tcl_GetBoolean where the value is false.

   graph:   Any Unicode printing character, except space.

   integer:   Any of the valid forms for an integer in Tcl, with optional surrounding whitespace. In case of under/overflow in the value, 0 is returned and the varname will contain -1.

   lower:   Any Unicode lower case alphabet character.

   print:   Any Unicode printing character, including space.

   punct:   Any Unicode punctuation character.

   space:   Any Unicode space character.

   true:   Any of the forms allowed to Tcl_GetBoolean where the value is true.

   upper:   Any upper case alphabet character in the Unicode character set.

   wordchar:   Any Unicode word character. That is any alphanumeric character, and any Unicode connector punctuation characters (e.g. underscore).

   xdigit:   Any hexadecimal digit character ([[0-9A-Fa-f]]). 

In the case of '''boolean''', '''true''' and '''false''', if the function will return '''0''', then the ''varname'' will always be set to '''0''', due to the varied nature of a valid boolean value.

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'''string is digit''' ''string'' will return 1 if ''string'' is composed of "Any Unicode digit character." Then it goes on to say that "this includes characters outside of the [[0-9]] range." What other characters, aside from [[0-9]], are members of the '''digit''' character class? 

[RS] As Tcl is great for [introspection], a few lines of code give the answer:
 proc udigits max {
   set res {}
   for {set i 0} {$i<=$max} {incr i} {
      if [string is digit [format %c $i]] {
         append res "\\u[format %04x $i] "
      }
   }
   set res
 }
 % udigits 65535
\u0030 \u0031 \u0032 \u0033 \u0034 \u0035 \u0036 \u0037 \u0038 \u0039 \u0660 \u0661 \u0662 \u0663 \u0664 \u0665 \u0666 \u0667 \u0668 \u0669 \u06f0 \u06f1 \u06f2 \u06f3 \u06f4 \u06f5 \u06f6 \u06f7 \u06f8 \u06f9 \u0966 \u0967 \u0968 \u0969 \u096a \u096b \u096c \u096d \u096e \u096f \u09e6 \u09e7 \u09e8 \u09e9 \u09ea \u09eb \u09ec \u09ed \u09ee \u09ef \u0a66 \u0a67 \u0a68 \u0a69 \u0a6a \u0a6b \u0a6c \u0a6d \u0a6e \u0a6f \u0ae6 \u0ae7 \u0ae8 \u0ae9 \u0aea \u0aeb \u0aec \u0aed \u0aee \u0aef \u0b66 \u0b67 \u0b68 \u0b69 \u0b6a \u0b6b \u0b6c \u0b6d \u0b6e \u0b6f \u0be7 \u0be8 \u0be9 \u0bea \u0beb \u0bec \u0bed \u0bee \u0bef \u0c66 \u0c67 \u0c68 \u0c69 \u0c6a \u0c6b \u0c6c \u0c6d \u0c6e \u0c6f \u0ce6 \u0ce7 \u0ce8 \u0ce9 \u0cea \u0ceb \u0cec \u0ced \u0cee \u0cef \u0d66 \u0d67 \u0d68 \u0d69 \u0d6a \u0d6b \u0d6c \u0d6d \u0d6e \u0d6f \u0e50 \u0e51 \u0e52 \u0e53 \u0e54 \u0e55 \u0e56 \u0e57 \u0e58 \u0e59 \u0ed0 \u0ed1 \u0ed2 \u0ed3 \u0ed4 \u0ed5 \u0ed6 \u0ed7 \u0ed8 \u0ed9 \u0f20 \u0f21 \u0f22 \u0f23 \u0f24 \u0f25 \u0f26 \u0f27 \u0f28 \u0f29 \u1040 \u1041 \u1042 \u1043 \u1044 \u1045 \u1046 \u1047 \u1048 \u1049 \u1369 \u136a \u136b \u136c \u136d \u136e \u136f \u1370 \u1371 \u17e0 \u17e1 \u17e2 \u17e3 \u17e4 \u17e5 \u17e6 \u17e7 \u17e8 \u17e9 \u1810 \u1811 \u1812 \u1813 \u1814 \u1815 \u1816 \u1817 \u1818 \u1819 \uff10 \uff11 \uff12 \uff13 \uff14 \uff15 \uff16 \uff17 \uff18 \uff19 

For instance, \u0660-\u0669 are "Indo-Arabic" digits as used in Arab countries. \uFF10-\uFF19 are "fullwidth" variants of 0-9, etc.

[Lars H]: Quite a lot, as you can see; there are plenty of digit sets in Unicode. The authorative source on the subject should be the Unicode Character Database (see [http://www.unicode.org/Public/UNIDATA/UCD.html] for format and links), but whether Tcl really uses that is another matter. A comparison of the above with the UCD shows that [[string is digit]] returns 1 for most (but not quite all!) of the characters from the class Nd (decimal digits), so that is probably what it is supposed to test.

''[escargo] 14 Mar 2006'' - I had my own peek starting at http://www.unicode.org/charts/symbols.html where there are links to
four PDF files under '''Numbers and Digits''': ASCII Digits, Fullwidth ASCII Digits, Number Forms, and Super and Subscripts.
All of these might legitimately contain digits.

[NEM] 14 Mar 2006: Interesting. Note though that most of these "digits" are not valid for
expressions fed to [expr]. So, if you are using [[string is digit]] to valid arguments to
expressions then you probably have a bug.

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See also:
   * [string]

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