use YAPE::Regex::Explain;
print YAPE::Regex::Explain->new(qr/999[89]\$/)->explain();

__END__

The regular expression:

(?-imsx:999[89]\$)

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):
----------------------------------------------------------------------
  999                      '999'
----------------------------------------------------------------------
  [89]                     any character of: '8', '9'
----------------------------------------------------------------------
  \$                       '$'
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------
[download]

Cheers,

Brent