要决定是否应该使用它，您应该了解它的功能以及是否需要它。这一点在我的回答中已经有了部分概述，我也对此做出了贡献。但是为了更容易理解和理解，这里有第二个解释。首先我们需要了解:
浏览器如何处理没有<BASE>被使用的链接?
对于一些例子，让我们假设我们有这些url:
一)http://www.example.com/index.html
B) http://www.example.com/
C) http://www.example.com/page.html
D) http://www.example.com/subdir/page.html
A和B都会将相同的文件(index.html)发送到浏览器，C当然发送page.html, D发送/subdir/page.html。
让我们进一步假设，两个页面都包含以下类型的链接:
完全限定的绝对链接(http://www…)
本地绝对链接(/some/dir/page.html)
相对链接，包括文件名(dir/page.html)和
只有“分段”的相对链接(#anchor， ?foo=bar)。
浏览器接收页面，并呈现HTML。如果它找到某个URL，它需要知道指向哪里。对于Link 1)来说，这一点总是很清楚的，因为它是按原样进行的。所有其他依赖于呈现页面的URL:
URL | Type | Result
--------+------+--------------------------
A,B,C,D | 2 | http://www.example.com/some/dir/page.html
A,B,C | 3 | http://www.example.com/dir/page.html
D | 3 | http://www.example.com/subdir/dir/page.html
A | 4 | http://www.example.com/index.html#anchor
B | 4 | http://www.example.com/#anchor
C | 4 | http://www.example.com/page.html#anchor
D | 4 | http://www.example.com/subdir/page.html#anchor
现在使用<BASE>会有什么变化?
<BASE>应该替换浏览器显示的URL。因此，它呈现所有链接，就好像用户调用了<BASE>中指定的URL一样。这解释了其他几个答案中的一些困惑:
again, nothing changes for "fully qualified absolute links" ("type 1")
for "local absolute links", the targeted server might change (if the one specified in <BASE> differs from the one being called initially from the user)
"relative URLs" become critical here, so you've got to take special care how you set <BASE>:
better avoid setting it to a directory.
Doing so, links of "type 3" (relative dir + filename) might continue to work, but it most certainly breaks those of "type 4" (relative + segment); except for "case B" (no path or filename).
setting it to the fully qualified file name produces, in most cases, the desired results.
举个例子最好地说明了这一点
假设你想用mod_rewrite“美化”一些URL:
<DOCUMENT_ROOT>/some/dir/file.php?lang = en
真实网址:http://www.example.com/some/dir/file.php?lang=en
友好的网址:http://www.example.com/en/file
让我们假设mod_rewrite用于透明地将用户友好的URL重写为真实的URL(没有外部重定向，因此“用户友好”的URL保留在浏览器的地址栏中，而真实的URL被加载)。现在该怎么办?
no <BASE> specified: breaks all relative links (as they would be based on http://www.example.com/en/file now)
<BASE HREF='http://www.example.com/some/dir>: Absolutely wrong. dir would be considered the file part of the specified URL, so still, all relative links are broken.
<BASE HREF='http://www.example.com/some/dir/>: Better already. But relative links of "type 4" are still broken (except for "case B").
<BASE HREF='http://www.example.com/some/dir/file.php>: Exactly. Everything should be working with this one.
最后一点
请记住，这适用于文档中的所有url:
< A HREF =
< IMG SRC =
< SCRIPT SRC =
.．.
