Buf_Switch(Buf_Free)
Win_Create(Buf_Num, 1, 1, 2, 14)
Ins_Text("Hello World! ")
#2 = Cur_Pos
Repeat(ALL) {
    if (Key_Shift_Status & 64) {
        BOL
        Block_Copy(#2-1, #2, DELETE)
    } else {
        Block_Copy(0, 1, DELETE)
    }
    EOL
    Update()
    Sleep(2)
}