The following equivalences to Unicode \p{} constructs and equivalent
    backslash character classes (if available), will hold:

        [:...:]     \p{...}         backslash

        alpha       IsAlpha
        alnum       IsAlnum
        ascii       IsASCII
        blank       IsSpace
        cntrl       IsCntrl
        digit       IsDigit        \d
        graph       IsGraph
        lower       IsLower
        print       IsPrint
        punct       IsPunct
        space       IsSpace
                    IsSpacePerl    \s
        upper       IsUpper
        word        IsWord
        xdigit      IsXDigit

    <em>For example "[:lower:]" and "\p{IsLower}" are equivalent.</em>

##</code><code>##

#!/usr/bin/perl
use strict;
use warnings;
$|++;

my %classes= qw/
  alpha IsAlpha
  alnum IsAlnum
  ascii IsASCII
  blank IsBlank
  cntrl IsCntrl
  digit IsDigit
  graph IsGraph
  lower IsLower
  print IsPrint
  punct IsPunct
  space IsSpace
  upper IsUpper
  word IsWord
  xdigit IsXDigit
/;

for( keys %classes )
{
  my( $r_posix, $r_unicode )= ( qr/[[:$_:]]/, qr/\p{$classes{$_}}/ );
  print "testing $r_posix and $r_unicode$/";
  for my $x (0x00..0x7e)
  {
    local $_= chr $x;
    printf "0x%x (%3d.) differ$/" => $x, $x 
      if /$r_posix/ xor /$r_unicode/;
  }
}
__END__
testing (?-xism:[[:digit:]]) and (?-xism:\p{IsDigit})
testing (?-xism:[[:upper:]]) and (?-xism:\p{IsUpper})
testing (?-xism:[[:xdigit:]]) and (?-xism:\p{IsXDigit})
testing (?-xism:[[:cntrl:]]) and (?-xism:\p{IsCntrl})
testing (?-xism:[[:alnum:]]) and (?-xism:\p{IsAlnum})
testing (?-xism:[[:space:]]) and (?-xism:\p{IsSpace})
testing (?-xism:[[:print:]]) and (?-xism:\p{IsPrint})
testing (?-xism:[[:ascii:]]) and (?-xism:\p{IsASCII})
testing (?-xism:[[:word:]]) and (?-xism:\p{IsWord})
testing (?-xism:[[:alpha:]]) and (?-xism:\p{IsAlpha})
testing (?-xism:[[:punct:]]) and (?-xism:\p{IsPunct})
0x24 ( 36.) differ
0x2b ( 43.) differ
0x3c ( 60.) differ
0x3d ( 61.) differ
0x3e ( 62.) differ
0x5e ( 94.) differ
0x60 ( 96.) differ
0x7c (124.) differ
0x7e (126.) differ
testing (?-xism:[[:lower:]]) and (?-xism:\p{IsLower})
testing (?-xism:[[:blank:]]) and (?-xism:\p{IsBlank})
testing (?-xism:[[:graph:]]) and (?-xism:\p{IsGraph})