[cairo] Docs
diff --git a/src/hb-cairo.cc b/src/hb-cairo.cc
index 5e2f471..b802698 100644
--- a/src/hb-cairo.cc
+++ b/src/hb-cairo.cc
@@ -730,6 +730,7 @@
  *
  * Extracts information from @buffer in a form that can be
  * passed to cairo_show_text_glyphs() or cairo_show_glyphs().
+ * This API is modeled after cairo_scaled_font_text_to_glyphs().
  *
  * See hb_cairo_font_face_set_scale_factor() for the details of
  * the @scale_factor argument.