shrink-to-fit和shrink-to-fit=no

在Bootstrap v4-alpha看到了shrink-to-fit=no，又出现了一个新的幺蛾子

<meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">

2017-03-12修改 - 理解错误，我好傻 
于是各种查，这一查，就是两天，因为shrink-to-fit和shrink-to-fit=no不一样，一个是没值的，一个有值的 

* 浏览器的shrink-to-fit是这个http://www.w3help.org/zh-cn/causes/RD8025 
* <meta>标签中的shrink-to-fit=no是这个http://div.io/topic/1409，下面说这个 

shrink-to-fit=no

下面的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.

参考

http://div.io/topic/1409 
https://developer.apple.com/library/content/releasenotes/General/WhatsNewInSafari/Articles/Safari_9_0.html#//apple_ref/doc/uid/TP40014305-CH9-SW36