Win class structure:
~~~~~~~~~~~~~~~~~~~~
create class Win from Box
  export:
  var Screen   //""
  var Visible  //false
  method New=WinNew      //o:New() --> self
  method Paint=WinPaint  //o:Paint(IsTop,lDouble) --> true
  method Show=WinShow    //o:Show() --> true
  method Hide=WinHide    //o:Hide() --> true
  method Done=WinDone    //o:Done() --> true
  endclass