Merge pull request #1349 from re-fort/add-description-about-event-modifier-passive

Add description and tip about `.passive` modifier

Author: sdras

src/v2/guide/events.md

@@ -205,6 +205,19 @@ To address this problem, Vue provides **event modifiers** for `v-on`. Recall tha
 
 Unlike the other modifiers, which are exclusive to native DOM events, the `.once` modifier can also be used on [component events](components.html#Using-v-on-with-Custom-Events). If you haven't read about components yet, don't worry about this for now.
 
+> New in 2.3.0+
+
+``` html
+<!-- the scroll event will not cancel the default scroll behavior -->
+<div v-on:scroll.passive="onScroll">...</div>
+```
+
+In addition to these modifiers, Vue provides `.passive` modifier to improve the performance on mobile especially.
+For example, when performing a scroll, the browser will scroll after the process has completed because the browser doesn’t know if the event is going to call `event.preventDefault()` within its handler.
+`.passive` modifier can be used to tell the browser that this event will not cancel the default event behavior in advance.
+
+<p class="tip">Don't use `.passive` and `.prevent` together. Passive handler can't prevent default event.</p>
+
 ## Key Modifiers
 
 When listening for keyboard events, we often need to check for common key codes. Vue also allows adding key modifiers for `v-on` when listening for key events: