HTTPヘッダーにCSSへのリンクを明示

This section only applies to user agents conforming to versions of HTTP that define a Link header field. Note that HTTP 1.1 as defined by [RFC2616] does not include a Link header field (refer to section 19.6.3).

Web server managers may find it convenient to configure a server so that a style sheet will be applied to a group of pages. The HTTP Link header has the same effect as a LINK element with the same attributes and values. Multiple Link headers correspond to multiple LINK elements occurring in the same order. For instance,

Link: <http://www.acme.com/corporate.css>; REL=stylesheet

corresponds to:

<LINK rel="stylesheet" href="http://www.acme.com/corporate.css">

現状どれだけ対応されているか知らないけど、外部CSSやらCSSハックって、全部これのUA判定でどーにかなるじゃん！！