docs(ngSwitch): clarify that ngSwitch matches against string literals

Closes #5285

Author: petebacondarwin

Diff for: src/ng/directive/ngSwitch.js

@@ -6,19 +6,26 @@
  * @restrict EA
  *
  * @description
- * The ngSwitch directive is used to conditionally swap DOM structure on your template based on a scope expression.
- * Elements within ngSwitch but without ngSwitchWhen or ngSwitchDefault directives will be preserved at the location
+ * The `ngSwitch` directive is used to conditionally swap DOM structure on your template based on a scope expression.
+ * Elements within `ngSwitch` but without `ngSwitchWhen` or `ngSwitchDefault` directives will be preserved at the location
  * as specified in the template.
  *
  * The directive itself works similar to ngInclude, however, instead of downloading template code (or loading it
- * from the template cache), ngSwitch simply choses one of the nested elements and makes it visible based on which element
+ * from the template cache), `ngSwitch` simply choses one of the nested elements and makes it visible based on which element
  * matches the value obtained from the evaluated expression. In other words, you define a container element
- * (where you place the directive), place an expression on the **on="..." attribute**
- * (or the **ng-switch="..." attribute**), define any inner elements inside of the directive and place
+ * (where you place the directive), place an expression on the **`on="..."` attribute**
+ * (or the **`ng-switch="..."` attribute**), define any inner elements inside of the directive and place
  * a when attribute per element. The when attribute is used to inform ngSwitch which element to display when the on
  * expression is evaluated. If a matching expression is not found via a when attribute then an element with the default
  * attribute is displayed.
  *
+ * <div class="alert alert-info">
+ * Be aware that the attribute values to match against cannot be expressions. They are interpreted
+ * as literal string values to match against.
+ * For example, **`ng-switch-when="someVal"`** will match against the string `"someVal"` not against the
+ * value of the expression `$scope.someVal`.
+ * </div>
+
  * @animations
  * enter - happens after the ngSwitch contents change and the matched child element is placed inside the container
  * leave - happens just after the ngSwitch contents change and just before the former contents are removed from the DOM
@@ -30,6 +37,7 @@
  *   <ANY ng-switch-default>...</ANY>
  * </ANY>
  *
+ *
  * @scope
  * @priority 800
  * @param {*} ngSwitch|on expression to match against <tt>ng-switch-when</tt>.