anchor.diff:   * `<a-j>`: join selected lines
    * `<a-J>`: join selected lines and select spaces inserted
               in place of line breaks
  - * `<a-m>`: merge contiguous selections together (works across lines as well)
  + * `<a-_>`: merge contiguous selections together (works across lines as well)
   
    * `<gt> (>)`: indent selected lines
    * `<a-gt>`: indent selected lines, including empty lines
  
positive.code: cursor.
  
  There is always at least one selection, and a selection is always at least
  one character (in which case the anchor and cursor of the selections are
  on the same character).
  
  Normal Mode
  
negative.code:             tabstop option or the count parameter for tabstop.
  
   * `<a-)>`: rotate selections content, if specified, the count groups
              selections, so `3<a-)>` rotate (1, 2, 3) and (4, 5, 6)
              independently.
   * `<a-(>`: rotate selections content backwards
  
  