add-completion-to-headadd-completion-to-head is a compiled Lisp function in `
completion.el'. (add-completion-to-head COMPLETION-STRING) If COMPLETION-STRING is not in the database, add it to prefix list. We add COMPLETION-STRING to the head of the appropriate prefix list, or to the head of the list. COMPLETION-STRING must be longer than `completion-prefix-min-length'. Updates the saved string with the supplied string. This must be very fast. Returns the completion entry.