+ * Fade the opacity of all matched elements to a specified opacity.
+ * Only the opacity is adjusted for this animation, meaning that
+ * all of the matched elements should already have some form of height
+ * and width associated with them.
+ *
+ * @example $("p").fadeTo("slow", 0.5);
+ *
+ * @name fadeTo
+ * @type jQuery
+ * @param Object speed A string representing one of the three predefined speeds ("slow", "normal", or "fast") or the number of milliseconds to run the animation (e.g. 1000).
+ * @param Number opacity The opacity to fade to (a number from 0 to 1).
+ */
+
+ /**
+ * Fade the opacity of all matched elements to a specified opacity and
+ * firing a callback function after completion.
+ * Only the opacity is adjusted for this animation, meaning that
+ * all of the matched elements should already have some form of height
+ * and width associated with them.
+ *
+ * @example $("p").fadeTo("slow", 0.5, function(){
+ * alert("Animation Done.");
+ * });
+ *
+ * @name fadeTo
+ * @type jQuery
+ * @param Object speed A string representing one of the three predefined speeds ("slow", "normal", or "fast") or the number of milliseconds to run the animation (e.g. 1000).
+ * @param Number opacity The opacity to fade to (a number from 0 to 1).
+ * @param Function callback A function to be executed whenever the animation completes.