Clean up the description of the mix algorithm.

lib/sass/script/functions.rb

@@ -947,23 +947,22 @@ def mix(color1, color2, weight = Number.new(50))
 
       Sass::Util.check_range("Weight", 0..100, weight, '%')
 
-      # This algorithm factors in both the user-provided weight
-      # and the difference between the alpha values of the two colors
-      # to decide how to perform the weighted average of the two RGB values.
+      # This algorithm factors in both the user-provided weight (w) and the
+      # difference between the alpha values of the two colors (a) to decide how
+      # to perform the weighted average of the two RGB values.
       #
       # It works by first normalizing both parameters to be within [-1, 1],
-      # where 1 indicates "only use color1", -1 indicates "only use color 0",
-      # and all values in between indicated a proportionately weighted average.
+      # where 1 indicates "only use color1", -1 indicates "only use color2", and
+      # all values in between indicated a proportionately weighted average.
       #
-      # Once we have the normalized variables w and a,
-      # we apply the formula (w + a)/(1 + w*a)
-      # to get the combined weight (in [-1, 1]) of color1.
+      # Once we have the normalized variables w and a, we apply the formula
+      # (w + a)/(1 + w*a) to get the combined weight (in [-1, 1]) of color1.
       # This formula has two especially nice properties:
       #
       #   * When either w or a are -1 or 1, the combined weight is also that number
       #     (cases where w * a == -1 are undefined, and handled as a special case).
       #
-      #   * When a is 0, the combined weight is w, and vice versa
+      #   * When a is 0, the combined weight is w, and vice versa.
       #
       # Finally, the weight of color1 is renormalized to be within [0, 1]
       # and the weight of color2 is given by 1 minus the weight of color1.