The regular expression:

(?m-isx:\A.*\nD$)

matches as follows:

NODE                     EXPLANATION
----------------------------------------------------------------------
(?m-isx:                 group, but do not capture (with ^ and $
                         matching start and end of line) (case-
                         sensitive) (with . not matching \n)
                         (matching whitespace and # normally):
----------------------------------------------------------------------
  \A                       the beginning of the string
----------------------------------------------------------------------
  .*                       any character except \n (0 or more times
                           (matching the most amount possible))
----------------------------------------------------------------------
  \n                       '\n' (newline)
----------------------------------------------------------------------
  D                        'D'
----------------------------------------------------------------------
  $                        before an optional \n, and the end of a
                           "line"
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------