diff --git a/focus-mode.el b/focus-mode.el
index 7e876d7..acdfa60 100644
--- a/focus-mode.el
+++ b/focus-mode.el
@@ -1,15 +1,24 @@
 (require 'cl-lib)
 
-(defvar-local focus-pre-overlay nil)
-(defvar-local focus-post-overlay nil)
+(defvar-local focus-pre-overlay nil
+  "The overlay that dims the text prior to the current-point.")
+
+(defvar-local focus-post-overlay nil
+  "The overlay that dims the text past the current-point.")
 
 (defun focus-search-backward (regex)
+  "A wrapper for re-search-backward, where the point does not move,
+and if the search fails, it returns NIL."
   (save-excursion (re-search-backward regex nil t)))
 
 (defun focus-search-forward (regex)
+  "A wrapper for re-search-backward, where the point does not move,
+and if the search fails, it returns NIL."
   (save-excursion (re-search-forward regex nil t)))
 
 (defun focus-average-colors (color &rest colors)
+  "This function takes one or more colors and returns the average
+of RGB values of the given colors."
   (let* ((colors (cons color colors))
          (colors (mapcar 'color-name-to-rgb colors))
          (len    (length colors))
@@ -18,12 +27,18 @@
     (apply 'color-rgb-to-hex avg)))
 
 (defun focus-move-focus ()
+  "If `focus-mode' is enabled, this command fires after each
+command, and moves the dimming overlays."
   (let* ((pre  (or (focus-search-backward "^\n") (point-min)))
          (post (or (focus-search-forward  "^\n") (point-max))))
     (move-overlay focus-pre-overlay  (point-min) pre)
     (move-overlay focus-post-overlay post (point-max))))
 
 (defun focus-init ()
+  "This function is run when focus-mode is enabled. It sets the
+`focus-pre-overlay' and `focus-post-overlay' to overlays; these
+are invisible until `focus-move-focus' is run. It adds
+focus-move-focus to `post-command-hook'."
   (setq focus-pre-overlay  (make-overlay (point-min) (point-min))
         focus-post-overlay (make-overlay (point-max) (point-max)))
   (let ((color (focus-average-colors
@@ -34,6 +49,9 @@
   (add-hook 'post-command-hook 'focus-move-focus nil t))
 
 (defun focus-terminate ()
+  "When `focus-mode' is disabled the overlays pointed to by
+`focus-pre-overlay' and `focus-post-overlay' are deleted, and
+`focus-move-focus' is removed from `post-command-hook'."
   (progn (mapc 'delete-overlay (list focus-pre-overlay focus-post-overlay))
          (remove-hook 'post-command-hook 'focus-move-focus t)))