— Variable: completion-at-point-functions

The value of this abnormal hook should be a list of functions, which are used to compute a completion table for completing the text at point. It can be used by major modes to provide mode-specific completion tables (see Major Mode Conventions).

When the command completion-at-point runs, it calls the functions in the list one by one, without any argument. Each function should return nil if it is unable to produce a completion table for the text at point. Otherwise it should return a list of the form

          (start end collection . props)

start and end delimit the text to complete (which should enclose point). collection is a completion table for completing that text, in a form suitable for passing as the second argument to try-completion (see Basic Completion); completion alternatives will be generated from this completion table in the usual way, via the completion styles defined in completion-styles (see Completion Variables). props is a property list for additional information; any of the properties in completion-extra-properties are recognized (see Completion Variables), as well as the following additional ones:

:predicate

The value should be a predicate that completion candidates need to satisfy.

:exclusive

If the value is no, then if the completion table fails to match the text at point, completion-at-point moves on to the next function in completion-at-point-functions instead of reporting a completion failure.

A function in completion-at-point-functions may also return a function. In that case, that returned function is called, with no argument, and it is entirely responsible for performing the completion. We discourage this usage; it is intended to help convert old code to using completion-at-point.

The first function in completion-at-point-functions to return a non-nil value is used by completion-at-point. The remaining functions are not called. The exception to this is when there is an :exclusive specification, as described above.

— Function: completion-in-region start end collection &optional predicate

This function completes the text in the current buffer between the positions start and end, using collection. The argument collection has the same meaning as in try-completion (see Basic Completion).

This function inserts the completion text directly into the current buffer. Unlike completing-read (see Minibuffer Completion), it does not activate the minibuffer.

For this function to work, point must be somewhere between start and end.