Regular Expression for Alphanumeric, float and Max Length in Multi Line

Alphanumeric with White space                                                  :- ^[a-zA-Z0-9 ]+$
For Float  length of integer part 9 and fraction part 4        :-  ([0-9]{1,8}(\.[0-9]{0,4})?|\.[0-9]{1,4})
Max Lenght  in MultiLine TExt BOX                                            :-  “^.{0,255}$”