docs(select): add more notes about ngRepeat and clean up style

Closes angular#9592

Author: jeffbcross

src/ng/directive/select.js

@@ -15,34 +15,37 @@ var ngOptionsMinErr = minErr('ngOptions');
  * elements for the `<select>` element using the array or object obtained by evaluating the
  * `ngOptions` comprehension_expression.
  *
+ * In many cases, `ngRepeat` can be used on `<option>` elements instead of `ngOptions` to achieve a
+ * similar result. However, the `ngOptions` provides some benefits such as reducing memory and
+ * increasing speed by not creating a new scope for each repeated instance, as well as providing
+ * more flexibility in how the `select`'s model is assigned via `select as`. `ngOptions should be
+ * used when the `select` model needs to be bound to a non-string value. This is because an option
+ * element can only be bound to string values at present.
+ *
  * When an item in the `<select>` menu is selected, the array element or object property
  * represented by the selected option will be bound to the model identified by the `ngModel`
  * directive.
  *
- * <div class="alert alert-warning">
- * **Note:** `ngModel` compares by reference, not value. This is important when binding to an
- * array of objects. See an example [in this jsfiddle](http://jsfiddle.net/qWzTb/).
- * </div>
- *
  * Optionally, a single hard-coded `<option>` element, with the value set to an empty string, can
  * be nested into the `<select>` element. This element will then represent the `null` or "not selected"
  * option. See example below for demonstration.
  *
  * <div class="alert alert-warning">
- * **Note:** `ngOptions` provides an iterator facility for the `<option>` element which should be used instead
- * of {@link ng.directive:ngRepeat ngRepeat} when you want the
- * `select` model to be bound to a non-string value. This is because an option element can only
- * be bound to string values at present.
+ * **Note:** `ngModel` compares by reference, not value. This is important when binding to an
+ * array of objects. See an example [in this jsfiddle](http://jsfiddle.net/qWzTb/).
  * </div>
  *
- * <div class="alert alert-info">
- * **Note:** Using `select as` will bind the result of the `select as` expression to the model, but
+ * ## `select as`
+ *
+ * Using `select as` will bind the result of the `select as` expression to the model, but
  * the value of the `<select>` and `<option>` html elements will be either the index (for array data sources)
- * or property name (for object data sources) of the value within the collection.
- * </div>
+ * or property name (for object data sources) of the value within the collection. If a `track by` expression
+ * is used, the result of that expression will be set as the value of the `option` and `select` elements.
+ *
+ * ### `select as` with `trackexpr`
+ *
+ * Using `select as` together with `trackexpr` is not recommended. Reasoning:
  *
- * **Note:** Using `select as` together with `trackexpr` is not recommended.
- * Reasoning:
  * - Example: &lt;select ng-options="item.subItem as item.label for item in values track by item.id" ng-model="selected"&gt;
  *   values: [{id: 1, label: 'aLabel', subItem: {name: 'aSubItem'}}, {id: 2, label: 'bLabel', subItem: {name: 'bSubItem'}}],
  *   $scope.selected = {name: 'aSubItem'};