use YAPE::Regex::Explain;
print YAPE::Regex::Explain->new(
    qr/[declaration_]?name="(.*?)"/
)->explain;
__END__
The regular expression:

(?-imsx:[declaration_]?name="(.*?)")

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):
----------------------------------------------------------------------
  [declaration_]?          any character of: 'd', 'e', 'c', 'l', 'a',
                           'r', 'a', 't', 'i', 'o', 'n', '_'
                           (optional (matching the most amount
                           possible))
----------------------------------------------------------------------
  name="                   'name="'
----------------------------------------------------------------------
  (                        group and capture to \1:
----------------------------------------------------------------------
    .*?                      any character except \n (0 or more times
                             (matching the least amount possible))
----------------------------------------------------------------------
  )                        end of \1
----------------------------------------------------------------------
  "                        '"'
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------
[download]

http://perldoc.perl.org/perlintro.html#Regular-expressions/perlrequick