The regular expression:

(?-imsx:^(\s^+)MVA)

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
----------------------------------------------------------------------
  (                        group and capture to \1:
----------------------------------------------------------------------
    \s                       whitespace (\n, \r, \t, \f, and " ")
----------------------------------------------------------------------
    ^+                       the beginning of the string (1 or more
                             times (matching the most amount
                             possible))
----------------------------------------------------------------------
  )                        end of \1
----------------------------------------------------------------------
  MVA                      'MVA'
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------