C:\>perl -MYAPE::Regex::Explain -e "print YAPE::Regex::Explain->new( '^[a-z]{3,10}\s*(?:\w{3,7}?\:\/\/[\w\-\.\/]*)??\/[\w\-\.\/~%@&=+$,;]*(?:\?[\S]*)??\s*http\/\d\.\d$')->explain"
The regular expression:

(?-imsx:^[a-z]{3,10}\s*(?:\w{3,7}?\:\/\/[\w\-\.\/]*)??\/[\w\-\.\/~%@&=+$,;]*(?:\?[\S]*)??\s*http\/\d\.\d$)

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):
----------------------------------------------------------------------
  ^                        the beginning of the string
----------------------------------------------------------------------
  [a-z]{3,10}              any character of: 'a' to 'z' (between 3
                           and 10 times (matching the most amount
                           possible))
----------------------------------------------------------------------
  \s*                      whitespace (\n, \r, \t, \f, and " ") (0 or
                           more times (matching the most amount
                           possible))
----------------------------------------------------------------------
  (?:                      group, but do not capture (optional
                           (matching the least amount possible)):
----------------------------------------------------------------------
    \w{3,7}?                 word characters (a-z, A-Z, 0-9, _)
                             (between 3 and 7 times (matching the
                             least amount possible))
----------------------------------------------------------------------
    \:                       ':'
----------------------------------------------------------------------
    \/                       '/'
----------------------------------------------------------------------
    \/                       '/'
----------------------------------------------------------------------
    [\w\-\.\/]*              any character of: word characters (a-z,
                             A-Z, 0-9, _), '\-', '\.', '\/' (0 or
                             more times (matching the most amount
                             possible))
----------------------------------------------------------------------
  )??                      end of grouping
----------------------------------------------------------------------
  \/                       '/'
----------------------------------------------------------------------
  [\w\-\.\/~%@&=+$,;]*     any character of: word characters (a-z, A-
                           Z, 0-9, _), '\-', '\.', '\/', '~', '%',
                           '@', '&', '=', '+', '$', ',', ';' (0 or
                           more times (matching the most amount
                           possible))
----------------------------------------------------------------------
  (?:                      group, but do not capture (optional
                           (matching the least amount possible)):
----------------------------------------------------------------------
    \?                       '?'
----------------------------------------------------------------------
    [\S]*                    any character of: non-whitespace (all
                             but \n, \r, \t, \f, and " ") (0 or more
                             times (matching the most amount
                             possible))
----------------------------------------------------------------------
  )??                      end of grouping
----------------------------------------------------------------------
  \s*                      whitespace (\n, \r, \t, \f, and " ") (0 or
                           more times (matching the most amount
                           possible))
----------------------------------------------------------------------
  http                     'http'
----------------------------------------------------------------------
  \/                       '/'
----------------------------------------------------------------------
  \d                       digits (0-9)
----------------------------------------------------------------------
  \.                       '.'
----------------------------------------------------------------------
  \d                       digits (0-9)
----------------------------------------------------------------------
  $                        before an optional \n, and the end of the
                           string
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------