The regular expression:

(?-imsx:[^\d+\.?\*?])

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):
----------------------------------------------------------------------
  [^\d+\.?\*?]             any character except: digits (0-9), '+',
                           '\.', '?', '\*', '?'
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------