[ReactNative] Improve PixelRatio documentation

Libraries/Utilities/PixelRatio.js

@@ -10,45 +10,49 @@ var Dimensions = require('Dimensions');
 /**
  * PixelRatio class gives access to the device pixel density.
  *
- * Some examples:
- *   - PixelRatio.get() === 2
- *     - iPhone 4, 4S
- *     - iPhone 5, 5c, 5s
- *     - iPhone 6
- *
- *   - PixelRatio.get() === 3
- *     - iPhone 6 plus
- *
  * There are a few use cases for using PixelRatio:
  *
- * == Displaying a line that's as thin as the device permits
+ * ### Displaying a line that's as thin as the device permits
  *
  * A width of 1 is actually pretty thick on an iPhone 4+, we can do one that's
- * thinner using a width of 1 / PixelRatio.get(). It's a technique that works
+ * thinner using a width of `1 / PixelRatio.get()`. It's a technique that works
  * on all the devices independent of their pixel density.
  *
- *   style={{ borderWidth: 1 / PixelRatio.get() }}
+ * ```
+ * style={{ borderWidth: 1 / PixelRatio.get() }}
+ * ```
  *
- * == Fetching a correctly sized image
+ * ### Fetching a correctly sized image
  *
  * You should get a higher resolution image if you are on a high pixel density
  * device. A good rule of thumb is to multiply the size of the image you display
  * by the pixel ratio.
  *
- *   var image = getImage({
- *     width: 200 * PixelRatio.get(),
- *     height: 100 * PixelRatio.get()
- *   });
- *   <Image source={image} style={{width: 200, height: 100}} />
+ * ```
+ * var image = getImage({
+ *   width: 200 * PixelRatio.get(),
+ *   height: 100 * PixelRatio.get()
+ * });
+ * <Image source={image} style={{width: 200, height: 100}} />
+ * ```
  */
 class PixelRatio {
+  /**
+   * Returns the device pixel density. Some examples:
+   *
+   *   - PixelRatio.get() === 2
+   *     - iPhone 4, 4S
+   *     - iPhone 5, 5c, 5s
+   *     - iPhone 6
+   *   - PixelRatio.get() === 3
+   *     - iPhone 6 plus
+   */
   static get() {
     return Dimensions.get('window').scale;
   }
+}
 
-  static startDetecting() {
-    // no-op for iOS, but this is useful for other platforms
-  }
-};
+// No-op for iOS, but used on the web. Should not be documented.
+PixelRatio.startDetecting = function() {};
 
 module.exports = PixelRatio;