-and END. Attributes specified by FACE take precedence over
-existing attributes. FACE must be a face name (a symbol or
-string), a property list of face attributes, or a list of these."
-
- (let ((pos start))
+and END in OBJECT (which defaults to the current buffer).
+Attributes specified by FACE take precedence over existing
+attributes unless BELOW is non-nil. FACE must be a face name (a
+symbol or string), a property list of face attributes, or a list
+of these. For convenience when applied to strings, this returns
+OBJECT."
+
+ ;; A face property can have three forms: a face name (a string or
+ ;; symbol), a property list, or a list of these two forms. In the
+ ;; list case, the faces will be combined, with the earlier faces
+ ;; taking precedent. Here we canonicalize everything to list form
+ ;; to make it easy to combine.
+ (let ((pos start)
+ (face-list (notmuch-face-ensure-list-form face)))