############################################################
The regular expression:

(?-imsx:(\.\d\d){5}?;)

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):
----------------------------------------------------------------------
  (                        group and capture to \1 (5 times):
----------------------------------------------------------------------
    \.                       '.'
----------------------------------------------------------------------
    \d                       digits (0-9)
----------------------------------------------------------------------
    \d                       digits (0-9)
----------------------------------------------------------------------
  ){5}?                    end of \1 (NOTE: because you're using a
                           quantifier on this capture, only the LAST
                           repetition of the captured pattern will be
                           stored in \1)
----------------------------------------------------------------------
  ;                        ';'
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------
############################################################
The regular expression:

(?-imsx:a{1,5})

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):
----------------------------------------------------------------------
  a{1,5}                   'a' (between 1 and 5 times (matching the
                           most amount possible))
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------
############################################################
The regular expression:

(?-imsx:a{1,5}?)

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):
----------------------------------------------------------------------
  a{1,5}?                  'a' (between 1 and 5 times (matching the
                           least amount possible))
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------