SVG xlink
http://www.w3.org/TR/SVG/linking.html
http://www.w3.org/TR/SVG/struct.html#UseElement
http://www.w3.org/TR/SVG/struct.html#ImageElement
http://stackoverflow.com/questions/3796025/fill-svg-path-element-with-a-background-image/3798797#3798797
http://dev.w3.org/SVG/profiles/1.2T/test/htmlEmbedHarness/struct-use-recursion-01-t.html
http://dev.w3.org/SVG/profiles/1.2T/test/svg/struct-use-recursion-01-t.svg
David: doesn't seem to work. SVG loaded from HTML doesn't follow xlinks in
Firefox; SVG loaded directly in Firefox only follows one level. I tried these
techniques:
<svg id="root" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" version="1.1">
  <circle cx="50" cy="50" r="49" stroke="black" stroke-width="2" fill="red"/>
  <use xlink:href="http://bamsoftware.com/tmp/2.svg#root"/>
</svg>
<svg id="root" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" version="1.1">
  <defs>
    <pattern id="pat" width="100" height="100">
      <image xlink:href="http://bamsoftware.com/tmp/2.svg"/>
    </pattern>
  </defs>
  <circle cx="50" cy="50" r="49" stroke="black" stroke-width="2" fill="url(#pat)"/>
</svg>

CSS @import
Requires us to change the model a bit: first request has to be for a .html
document; thereafter requests for .css documents.
https://developer.mozilla.org/en-US/docs/CSS/@import

Link prefetch
<link rel=prefetch href="http://example.com/">
http://www.whatwg.org/specs/web-apps/current-work/#link-type-prefetch