cmpl-prefix-entry-head

cmpl-prefix-entry-head is an alias for `car' in `completion.el'.

(cmpl-prefix-entry-head LIST)

Return the car of LIST. If arg is nil, return nil.
Error if arg is not nil and not a cons cell. See also `car-safe'.

See Info node `(elisp)Cons Cells' for a discussion of related basic
Lisp concepts such as car, cdr, cons cell and list.