MarkColumn          <Alt K>
    -------------------------------------------------------------------------

    This command is used to mark a column Block.  Initially executing
    this command will mark the current cursor position.  As the cursor
    is moved, the Block will "grow".  Executing this command again will
    mark the other end of the Block at the current cursor position.  If
    MarkColumn is executed in a file that already contains a Block, the
    Block is extended to the current cursor position.