HTTP_X_PURPOSE 的定义是什么？
最近，我们一直在查看 Stack Overflow 日志中捕获的一些异常，并发现了 Safari 用户的问题。
我在我们捕获的异常之一中注意到了这个 HTTP 标头：
HTTP_X_PURPOSE preview
有谁知道什么操作会触发此标头或 HTTP_X_PURPOSE 的含义？
Recently we've been looking at a few exceptions captured in our Stack Overflow logs and have discovered an issue for Safari users.
I noticed this HTTP header in one of the exceptions we have captured:
HTTP_X_PURPOSE preview
Does anyone know what action triggers this header or the meaning of HTTP_X_PURPOSE?
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“X-Purpose：预览”标题绝对是 Safari 4 顶级网站的东西。 “热门站点”页面尝试显示最喜欢的页面的实时缩略图。如果在选项卡中打开最喜欢的页面，它会从该页面的当前版本中获取缩略图。如果某个页面在打开的选项卡中不可用，并且缩略图已经过时*，它会发出后台请求以获取该页面的当前版本。
X-Purpose：预览标头仅附加到 base URL 的 HTTP 请求。它不附加到页面引用的资源（JS/CSS/images/flash）。
我刚刚在这里写了一篇关于此的博客文章： https://web.archive.org/web/20131115045854/https://web.archive.org/web/20131115045854/https:/ /sunpig.com/martin/archives/2010/01/08/how-to-detect-a-page-request-from-safari-4s-top-sites-feature.html
（*我没有探索了其“足够过时”的标准。）
The "X-Purpose: preview" header is definitely a Safari 4 top sites thing. The Top Sites page tries to show a live-ish thumbnail of the favourite pages. If favourite page is open in a tab, it grabs a thumbnail from the current version of the page. If a page is not available in an open tab, and the thumbnail is sufficiently out of date*, it makes a background request to get the current version of the page.
The X-Purpose: preview header is only attached to the HTTP request for the base URL. It is not attached to the resources (JS/CSS/images/flash) referenced on the page.
I've just written a blog entry on this over here: https://web.archive.org/web/20131115045854/https://sunpig.com/martin/archives/2010/01/08/how-to-detect-a-page-request-from-safari-4s-top-sites-feature.html
(* I haven't explored its criteria for "sufficiently out of date" yet.)
渲染 Safari 4.0 热门站点显示模式时可能会发送？没有测试过，只是猜测。
Might be sent when rendering for the Safari 4.0 Top Sites display mode? Haven't tested, just a guess.