The regex has no syntax that was added after Perl version 5.6, so YAPE::Regex::Explain may be helpful.

c:\@Work\Perl\monks>perl -wMstrict -le
"use YAPE::Regex::Explain;
 ;;
 my $rx = qr/[(](\w+)[^(]+[(](\w+)[^:]+:\s+(\w+).*?slack[^-]+(-\d+)/s;
 ;;
 print YAPE::Regex::Explain->new($rx)->explain;
"
The regular expression:

(?s-imx:[(](\w+)[^(]+[(](\w+)[^:]+:\s+(\w+).*?slack[^-]+(-\d+))

matches as follows:

NODE                     EXPLANATION
----------------------------------------------------------------------
(?s-imx:                 group, but do not capture (with . matching
                         \n) (case-sensitive) (with ^ and $ matching
                         normally) (matching whitespace and #
                         normally):
----------------------------------------------------------------------
  [(]                      any character of: '('
----------------------------------------------------------------------
  (                        group and capture to \1:
----------------------------------------------------------------------
    \w+                      word characters (a-z, A-Z, 0-9, _) (1 or
                             more times (matching the most amount
                             possible))
----------------------------------------------------------------------
  )                        end of \1
----------------------------------------------------------------------
  [^(]+                    any character except: '(' (1 or more times
                           (matching the most amount possible))
----------------------------------------------------------------------
  [(]                      any character of: '('
----------------------------------------------------------------------
  (                        group and capture to \2:
----------------------------------------------------------------------
    \w+                      word characters (a-z, A-Z, 0-9, _) (1 or
                             more times (matching the most amount
                             possible))
----------------------------------------------------------------------
  )                        end of \2
----------------------------------------------------------------------
  [^:]+                    any character except: ':' (1 or more times
                           (matching the most amount possible))
----------------------------------------------------------------------
  :                        ':'
----------------------------------------------------------------------
  \s+                      whitespace (\n, \r, \t, \f, and " ") (1 or
                           more times (matching the most amount
                           possible))
----------------------------------------------------------------------
  (                        group and capture to \3:
----------------------------------------------------------------------
    \w+                      word characters (a-z, A-Z, 0-9, _) (1 or
                             more times (matching the most amount
                             possible))
----------------------------------------------------------------------
  )                        end of \3
----------------------------------------------------------------------
  .*?                      any character (0 or more times (matching
                           the least amount possible))
----------------------------------------------------------------------
  slack                    'slack'
----------------------------------------------------------------------
  [^-]+                    any character except: '-' (1 or more times
                           (matching the most amount possible))
----------------------------------------------------------------------
  (                        group and capture to \4:
----------------------------------------------------------------------
    -                        '-'
----------------------------------------------------------------------
    \d+                      digits (0-9) (1 or more times (matching
                             the most amount possible))
----------------------------------------------------------------------
  )                        end of \4
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------
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Update: Also see davido's on-line Perl Regular Expression Tester for post-5.6 syntax.