戴夫·沃德说，
It’s not exactly light reading, but section 4.2 of RFC 3986 provides for fully qualified URLs that omit protocol (the HTTP or HTTPS) altogether. When a URL’s protocol is omitted, the browser uses the underlying document’s protocol instead.
Put simply, these “protocol-less” URLs allow a reference like this to work in every browser you’ll try it in:
//ajax.googleapis.com/ajax/libs/jquery/1.4.4/jquery.min.js
It looks strange at first, but this “protocol-less” URL is the best way to reference third party content that’s available via both HTTP and HTTPS.
这当然可以解决我们在HTTP页面上看到的一堆混合内容错误——假设我们的资产可以通过HTTP和HTTPS使用。
这是完全跨浏览器兼容的吗?还有其他注意事项吗?
在发布前我进行了彻底的测试。在所有可以在Browsershots上测试的浏览器中，我只能找到一个不能正确处理协议相对URL的浏览器:一个名为Dillo的*nix浏览器。
我收到的反馈有两个缺点:
Protocol-less URLs may not work as expected when you "open" a local file in your browser, because the page's base protocol will be file:///. Especially when you're using the protocol-less URL for an external resource like a CDN-hosted asset. Using a local web server like Apache or IIS to test against http://localhost addresses works fine though.
Apparently there's at least one iPhone feed reader app that does not handle the protocol-less URLs correctly. I'm not aware of which one has the problem or how popular it is. For hosting a JavaScript file, that's not a big problem since RSS readers typically ignore JavaScript content anyway. However, it could be an issue if you're using these URLs for media like images inside content that needs to be syndicated via RSS (though, this single reader app on a single platform probably accounts for a very marginal number of readers).
