(defface completions-first-difference
'((t (:inherit bold)))
- "Face added on the first uncommon character in completions in *Completions* buffer.")
+ "Face for the first uncommon character in completions.
+See also the face `completions-common-part'.")
(defface completions-common-part '((t nil))
- "Face added on the common prefix substring in completions in *Completions* buffer.
-The idea of `completions-common-part' is that you can use it to
-make the common parts less visible than normal, so that the rest
-of the differing parts is, by contrast, slightly highlighted.")
-
-(defun completion-hilit-commonality (completions prefix-len base-size)
+ "Face for the common prefix substring in completions.
+The idea of this face is that you can use it to make the common parts
+less visible than normal, so that the differing parts are emphasized
+by contrast.
+See also the face `completions-first-difference'.")
+
+(defun completion-hilit-commonality (completions prefix-len &optional base-size)
+ "Apply font-lock highlighting to a list of completions, COMPLETIONS.
+PREFIX-LEN is an integer. BASE-SIZE is an integer or nil (meaning zero).
+
+This adds the face `completions-common-part' to the first
+\(PREFIX-LEN - BASE-SIZE) characters of each completion, and the face
+`completions-first-difference' to the first character after that.
+
+It returns a list with font-lock properties applied to each element,
+and with BASE-SIZE appended as the last element."
(when completions
(let ((com-str-len (- prefix-len (or base-size 0))))
(nconc