COPY BLOCK TO BUFFER                                               <Alt>+C

  You can use this option to copy a section of the screen to a buffer for
  later retrieval. Use the arrow keys, <Home>, <End>, <PgUp> and <PgDn> to
  resize the box specifying the area to be copied. <Tab> toggles between the
  top left and the bottom right corners when resizing. Press <Enter> when
  you are ready to copy, or press <Esc> to abort the operation.

  Once you press <Enter>, you will be required to choose which of the nine
  buffers to copy to. The ones marked with an X are unused, the ones marked
  with a . contain data. You can still copy into buffer containing data,
  however the data that was previously there will obviously be lost.