The first one, with the name of page_title, allows you to override the value for the header of the page.

第一个的名称是page _ title，允许您重写页眉的值。

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A first-time visitor to your page may have to make several HTTP requests, but by using the Expires header you make those components cacheable.

首次访客到的网页可能要几个的HTTP请求，但通过使用Expires标题您使这些组件缓存。

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Refback. When a Web browser user clicks a link from one page to another, the request to the second site includes an HTTP header called the referrer, with the URL of the first page.

refback：当web浏览器用户单击链接从一个页面转到另一个页面时，对第二个页面的请求包含一个http头(它被称为referrer)以及第一个页面的URL。

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