of-contents__link toc-highlight">2.1 Expires</a></li><li><a href="#22-cache-control" class="table-of-contents__link toc-highlight">2.2 Cache-Control</a></li><li><a href="#23-拓展知识冷门考点" class="table-of-contents__link toc-highlight">2.3 拓展知识（冷门考点）</a></li></ul></li><li><a href="#3-协商缓存" class="table-of-contents__link toc-highlight">3. 协商缓存</a><ul><li><a href="#31-etag--if-none-match" class="table-of-contents__link toc-highlight">3.1 ETag / If-None-Match</a></