#!/usr/bin/perl --
use YAPE::Regex::Explain;
print YAPE::Regex::Explain->new( qr/^_*((\d*|#*|\**)+(\[\d+\-\d\])?)(X*\.?\!?)$/ )->explain;
__END__
The regular expression:

(?-imsx:^_*((\d*|#*|\**)+(\[\d+\-\d\])?)(X*\.?!?)$)

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
----------------------------------------------------------------------
  _*                       '_' (0 or more times (matching the most
                           amount possible))
----------------------------------------------------------------------
  (                        group and capture to \1:
----------------------------------------------------------------------
    (                        group and capture to \2 (1 or more times
                             (matching the most amount possible)):
----------------------------------------------------------------------
      \d*                      digits (0-9) (0 or more times
                               (matching the most amount possible))
----------------------------------------------------------------------
     |                        OR
----------------------------------------------------------------------
      #*                       '#' (0 or more times (matching the
                               most amount possible))
----------------------------------------------------------------------
     |                        OR
----------------------------------------------------------------------
      \**                      '*' (0 or more times (matching the
                               most amount possible))
----------------------------------------------------------------------
    )+                       end of \2 (NOTE: because you're using a
                             quantifier on this capture, only the
                             LAST repetition of the captured pattern
                             will be stored in \2)
----------------------------------------------------------------------
    (                        group and capture to \3 (optional
                             (matching the most amount possible)):
----------------------------------------------------------------------
      \[                       '['
----------------------------------------------------------------------
      \d+                      digits (0-9) (1 or more times
                               (matching the most amount possible))
----------------------------------------------------------------------
      \-                       '-'
----------------------------------------------------------------------
      \d                       digits (0-9)
----------------------------------------------------------------------
      \]                       ']'
----------------------------------------------------------------------
    )?                       end of \3 (NOTE: because you're using a
                             quantifier on this capture, only the
                             LAST repetition of the captured pattern
                             will be stored in \3)
----------------------------------------------------------------------
  )                        end of \1
----------------------------------------------------------------------
  (                        group and capture to \4:
----------------------------------------------------------------------
    X*                       'X' (0 or more times (matching the most
                             amount possible))
----------------------------------------------------------------------
    \.?                      '.' (optional (matching the most amount
                             possible))
----------------------------------------------------------------------
    !?                       '!' (optional (matching the most amount
                             possible))
----------------------------------------------------------------------
  )                        end of \4
----------------------------------------------------------------------
  $                        before an optional \n, and the end of the
                           string
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------