View:PreGoto(Menu,MdId): public: return true
  Prevalid (when) function called from a menu to validate the atempt
  of method View:Goto() activation.

  Parameter description:
  ~~~~~~~~~~~~~~~~~~~~~~
  Menu: object_of_Menu: no default.
   Menu which requests the validity test and sends self to the method.

  MdId: numeric: no default.
   The MenuDataID number for setting the data structure of Menu object to
   prevalidate.