All the regex operators you're using in the OPed examples are supported by Perl version 5.6 and before, so you could also have used YAPE::Regex::Explain (which only supports regexes through Perl version 5.6) to give you some insight:

c:\@Work\Perl>perl -wMstrict -le
"use YAPE::Regex::Explain;
 ;;
 print YAPE::Regex::Explain->new(qr/[need]+$/)->explain;
"
The regular expression:

(?-imsx:[need]+$)

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):
----------------------------------------------------------------------
  [need]+                  any character of: 'n', 'e', 'e', 'd' (1 or
                           more times (matching the most amount
                           possible))
----------------------------------------------------------------------
  $                        before an optional \n, and the end of the
                           string
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------
[download]

(Note, however, that this explanation does not make clear the point already made by BrowserUk ++here that the  [need] character set only encompasses three characters  n e d and has nothing to do with a sequence 'need'.)