anchor.diff:   * _?_: search (extend to next match)
    * _n_: select next match
    * _N_: add a new selection with next match
  - * _alt-n_: replace last selection with next match (preserving the others)
  -
  - * _alt-c_: center last selection in current window
  + * _alt-n_: replace main selection with next match (preserving the others)
  +
  + * _alt-c_: center main selection in current window
    * _pageup_: scroll up
    * _pagedown_: scroll down
   
  
positive.code:      to execute when the item is selected (but not validated).
   * +info <text>+: display text in an information box, at can take a -anchor
       option, which accepts +left+, +right+ and +cursor+ as value, in order to
       specify where the info box should be anchored relative to the last selection.
   * +try <commands> catch <on_error_commands>+: prevent an error in <commands>
       from aborting the whole commands execution, execute <on_error_commands>
       instead.
  
negative.code: :hook global WinCreate .*\.cc %{ addhl number_lines }
  -----------------------------------------------------
  
  existing hooks are:
  
   * +NormalIdle+: A certain duration has passed since last key was pressed in
         normal mode.
   * +NormalBegin+: Entering normal mode
   * +NormalEnd+: Leaving normal mode
   * +NormalKey+: A key is received in normal mode, the key is used for filtering
   * +InsertIdle+: A certain duration has passed since last key was pressed in
         insert mode.
   * +InsertBegin+: Entering insert mode
   * +InsertEnd+: Leaving insert mode
   * +InsertKey+: A key is received in insert mode, the key is used for filtering
   * +InsertMove+: The cursor moved (without inserting) in insert mode, the key
         that triggered the move is used for filtering
   * +WinCreate+: A window was created
   * +WinSetOption+: An option was set in a window context, the filtering text
         is '<option_name>=<new_value>'
   * +BufNew+: A buffer for a new file has been created, filename is used for
         filtering
   * +BufOpen+: A buffer for an existing file has been created, filename is
         used for filtering
   * +BufCreate+: A buffer has been created, filename is used for filtering
   * +RuntimeError+: an error was encountered while executing an user command
         the error message is used for filtering
  
  when not specified, the filtering text is an empty string.
  
  Shell expansion
  ---------------
  
  