?..
  bcs @error_in_escape_seq   ; ..error!
  sty temp_ptr_x ; save top      
  ; -- prepare bottom --
  jsr get_number_from_esc_seq
  ldy escape_parameter    ; get bottom
  dey         ; line 1 -> line 0
  cpy #$19    ; >=25?..
  bcs @error_in_escape_seq   ; ..error! 
  sty temp_ptr_y ; save bottom       
  ; -- validate lines --
  lda temp_ptr_x ; restore top
  cmp temp_ptr_y ; >= bottom?..
  bcs @error_in_escape_seq   ; ..error!
  sta scroll_region_start     ; top -> SRStart
  sty scroll_r