shrink-to-fit(自适应宽度)

下面一行代码可以让网页的宽度自动适应手机屏幕的宽度

<meta name="viewport" content="width=device-width,initial-scale=1">

但在IOS9中要想起作用，得加上"shrink-to-fit=no"，原因如下：

Viewport meta tags using"width=device-width" cause the page to scale down to fit content that overflows the viewport bounds. 
You can override this behavior by adding "shrink-to-fit=no" to your meta tag as shown below. 
The added value will prevent the page from scaling to fit the viewport.