3. Key bindings

While in lightning completion, the behavior of each key is modified. Here is a description of what each key does; these functions are loosely based on the behavior of standard completion in Emacs. I have also included examples; for all of the examples, suppose that you are completing on file names, and you have files `albatross', `alpo', `alphabet', and `alphabet-soup'.

There is a customizable variable lc-complete-idle-time-default, the default value of which is 0.5. In lightning completion mode, after this number of seconds of idle time, Emacs tries to complete.

• a-z, A-Z, 0-9, etc.: After the delay, you get an error if there is no valid completion based on that character. If there are valid completions, then Emacs inserts the characters in common with all the valid completions. If there is a unique such completion, then Emacs inserts that completion, and completion stops. (Example: if you have `alp' and you hit x, you get an error (but you're still in lightning completion mode); if you hit h, then `habet' is inserted, resulting in `alphabet' (and you're still in lightning completion mode). If you then hit -, then `-soup' is inserted, and completion stops.)

  When there are no valid completions, the value of the customizable variable lc-clean-up is relevant. If it is nil, then Emacs beeps and warns you that there are no valid completions. If it is non-nil, then in addition, Emacs deletes the offending characters. (Example: if you have `alp' and you hit x, then `x' is inserted. If lc-clean-up is nil, then Emacs beeps. If lc-clean-up is non-nil, then Emacs beeps and deletes the `x'. If you have `al' and you type phx, if lc-clean-up is non-nil, then the `x' is deleted and `abet' is inserted.)

• SPC: If you have a valid completion, this key ends lightning completion, keeping the current completion; otherwise, if there is a valid completion based on the current string together with " ", then a space is inserted. Otherwise, SPC acts like the TAB key. (Example: if you have `alp' and you hit h, resulting in `alphabet', then hitting SPC would end completion and do nothing else. If you also have a file `al jolson', then typing `al' followed by SPC produces `al jolson'. Typing `alp' followed by SPC is just like typing `alp' and hitting TAB.)

• RET: This key exits lightning completion, regardless of whether you have a valid completion, and inserts a new line or exits the minibuffer, whichever is appropriate. (Example: if you are using have `alp' and you hit RET, this ends completion and either inserts a new line or exits the minibuffer.) (This is actually an example of the behavior of "Other control characters," described below.)

• DEL: This deletes the last thing that was typed along with anything inserted automatically as a result. (Example: if you had `alp' and you hit h, resulting in `alphabet', then hitting DEL would delete `habet'---the characters that were just inserted.)

• C-f: Hitting this key repeatedly cycles through the possible completions, in some order or other. (Example: if you have `a', then hitting C-f once will give `albatross'; hitting it again will give `alpo', etc.)

• C-b: This works like C-f, but it cycles through the choices in the reverse order.

• TAB: Hitting this key completes as far as possible. If there are several choices, then it opens up a new buffer in another window, called *Completions*, in which all of the valid completions are displayed. That buffer is buried once completion ends. (Example, if I have `alp' and I hit TAB, then a new buffer opens up, containing `alpo', `alphabet', and `alphabet-soup'. If I then hit h and then TAB, the *Completions* buffer then displays `alphabet' and `alphabet-soup'.) You can select a completion by clicking on it with mouse-2.

• M-v: Hitting this key opens up a new buffer in another window, called *Completions*, just as with the TAB key, but also moves the point to that window. You can then move from one completion choice to another with the arrow keys, and you can select a completion with RET or with mouse-2.

• C-c: Hitting this key exits lightning completion mode (useful if you've had enough of this completion nonsense, and you just want to type in the file name yourself; also useful if you want to type in the name of a file that doesn't exist).

• C-q: This key quotes the next character (useful if you have a file name containing a control character like C-c or TAB, for instance).

• C-h: Hitting this key displays a very brief help message in the minibuffer.

• Other control characters: Hitting any other control character (or other non-printing character) has two effects: completion stops, and that character then has its normal effect. So C-g stops completion and beeps, C-e stops completion and moves you to the end of the line, etc.

Many of these keys can be customized (in the customization group lightning-completion-keys).