c:\@Work\Perl\monks>perl -wMstrict -le
"use YAPE::Regex::Explain;
 ;;
 print YAPE::Regex::Explain->new('(?:\s+|$)')->explain;
 ;;
 my $password = 'f+o*o?[ ]b{}r';
 my $regex = qr/Password=\Q$password\E/;
 print YAPE::Regex::Explain->new($regex)->explain;
"
The regular expression:

(?-imsx:(?:\s+|$))

matches as follows:

NODE                     EXPLANATION
----------------------------------------------------------------------
(?-imsx:                 group, but do not capture (case-sensitive)
                         (with ^ and $ matching normally) (with . not
                         matching \n) (matching whitespace and #
                         normally):
----------------------------------------------------------------------
  (?:                      group, but do not capture:
----------------------------------------------------------------------
    \s+                      whitespace (\n, \r, \t, \f, and " ") (1
                             or more times (matching the most amount
                             possible))
----------------------------------------------------------------------
   |                        OR
----------------------------------------------------------------------
    $                        before an optional \n, and the end of
                             the string
----------------------------------------------------------------------
  )                        end of grouping
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------

The regular expression:

(?-imsx:Password=f\+o\*o\?\[\ \]b\{\}r)

matches as follows:

NODE                     EXPLANATION
----------------------------------------------------------------------
(?-imsx:                 group, but do not capture (case-sensitive)
                         (with ^ and $ matching normally) (with . not
                         matching \n) (matching whitespace and #
                         normally):
----------------------------------------------------------------------
  Password=f               'Password=f'
----------------------------------------------------------------------
  \+                       '+'
----------------------------------------------------------------------
  o                        'o'
----------------------------------------------------------------------
  \*                       '*'
----------------------------------------------------------------------
  o                        'o'
----------------------------------------------------------------------
  \?                       '?'
----------------------------------------------------------------------
  \[                       '['
----------------------------------------------------------------------
  \                        ' '
----------------------------------------------------------------------
  \]                       ']'
----------------------------------------------------------------------
  b                        'b'
----------------------------------------------------------------------
  \{                       '{'
----------------------------------------------------------------------
  \}                       '}'
----------------------------------------------------------------------
  r                        'r'
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------