Task:DoneBlock: public: code_block
  Here can be code block placed to do the window closing connected job.
  (i.g. saving of changed text). If it returns true the object (class)
  can be destroyed, if false it can't be destroyed and the control is
  passed to virtual process of this task from the task swapper.
  When calling the code block Task:DoneBlock is the object
  of instvar variable Doneblock passed as a parameter.