Choice class structure:
~~~~~~~~~~~~~~~~~~~~~~~~
create class Choice from Win
  export:
  var Items      //{"item1",...}
  var SelItems   //{lSelectable,...}
  var Cursor     //(object of Cursor)
  var Choice     //1
  var Top        //1
  var CanAppend  //false
  var InsBlock   //{|o|nil}
  var DelBlock   //{|o|nil}
  var InRow      //0
  var InCol      //0
  var InCurSize  //0
  method New=ChoiceNew           //o:New() --> self
  method Init=ChoiceInit         //o:Init(Name,R,C,CurSize,Items,SelItems,Clr,Shd) --> true
  method FastInit=ChoiceFastInit //o:FastInit(Name,R,C,CurSize,Items,SelItems,Clr,Shd) --> true
  method Process=ChoiceProcess   //o:Process() --> nChoice
  method Done=ChoiceDone         //o:Done() --> true
  endclass