The regular expression:

(?-imsx:^<\/script>\s+-->)

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
----------------------------------------------------------------------
  <                        '<'
----------------------------------------------------------------------
  \/                       '/'
----------------------------------------------------------------------
  script>                  'script>'
----------------------------------------------------------------------
  \s+                      whitespace (\n, \r, \t, \f, and " ") (1 or
                           more times (matching the most amount
                           possible))
----------------------------------------------------------------------
  -->                      '-->'
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------