diff --git a/why-this.el b/why-this.el
index 287ee99921..19acb90f9f 100644
--- a/why-this.el
+++ b/why-this.el
@@ -36,6 +36,10 @@
 (require 'timezone)
 (require 'color)
 
+;; A very high-level request that would probably take too much work to
+;; actualise, would be to figure out some way to integrate this into
+;; VC.  That way you can make use of this even if you don't use Git or Hg.
+
 (defgroup why-this nil
   "Show why the current line contains this."
   :group 'tools
@@ -64,6 +68,7 @@ the first argument is the command (which is a symbol):
     `:author'   Name of the author.
     `:time'     Time of change (local).
     `:desc'     Single line description of change."
+  ;; Would it make sense to use a `cl-defstruct'?
   :type 'hook
   :options (list #'why-this-git
                  #'why-this-hg)
@@ -326,6 +331,7 @@ TIME-FORMAT is used to format data."
              (?t . (why-this-format-time
                     time-format (plist-get data :time)))
              (?i . (plist-get data :desc)))))
+      ;; `format-spec' should make this simpler
       (replace-regexp-in-string
        "%."
        (lambda (str)
@@ -342,7 +348,7 @@ TIME-FORMAT is used to format data."
 (defun why-this--overlay-bg-type (pos)
   "Return the background type for overlay at POS."
   (cond
-   ((and (use-region-p)
+   ((and (use-region-p)                         ;perhaps `region-active-p'?
          (>= pos (region-beginning))
          (< pos (region-end)))
     'region)
@@ -364,6 +370,7 @@ TIME-FORMAT is used to format data."
                    'solaire-region-face
                  'region))
               ('line
+               ;; Looks like a `cond' to me
                (if (bound-and-true-p hl-line-mode)
                    (if (bound-and-true-p solaire-mode)
                        'solaire-hl-line-face
@@ -382,12 +389,10 @@ TIME-FORMAT is used to format data."
   (while why-this--overlays
     (delete-overlay (pop why-this--overlays)))
   (when why-this-mode
-    (let* ((begin (line-number-at-pos (if (use-region-p)
-                                          (region-beginning)
-                                        (point))))
-           (end (1+ (line-number-at-pos (if (use-region-p)
-                                            (region-end)
-                                          (point)))))
+    (let* ((line (line-number-at-pos (if (use-region-p)
+                                         (region-beginning)
+                                       (point))))
+           (begin line) (end (1+ line))
            (backend why-this--backend)
            (data (funcall backend 'line-data begin end)))
       (dolist (i (number-sequence 0 (- end begin 1)))
@@ -446,6 +451,8 @@ TIME-FORMAT is used to format data."
                                          (region-end)
                                        (point))))))
     (setq
+     ;; Perhaps this could be made more readble by using
+     ;; `thread-last' or the above let binding
      why-this--overlays
      (delq
       nil
@@ -458,10 +465,10 @@ TIME-FORMAT is used to format data."
                          (< line end)
                          (eq line (overlay-get ov 'why-this-line)))))
              (progn
-               (let* ((ov-start (overlay-start ov))
-                      line-begin
-                      line-end
-                      column)
+               (let ((ov-start (overlay-start ov))
+                     line-begin
+                     line-end
+                     column)
                  (save-excursion
                    (goto-char ov-start)
                    (setq line-begin (line-beginning-position))
@@ -537,6 +544,11 @@ Actually the supported backend is returned."
                    (* (- (nth i b-color)
                          (nth i a-color))
                       ratio)))))
+    ;; Note that RGB interpolation doesn't always behave the way you
+    ;; think it does.  You'd have to convert it into some other color
+    ;; space like CIELAB to get perceptual mixing right (but even that
+    ;; is trying because it requires some kind of a white-reference
+    ;; point).
     (color-rgb-to-hex (funcall mix 0)
                       (funcall mix 1)
                       (funcall mix 2)