Apache Reference: mod_rewrite, RewriteBase
Rewrite URL Base
Syntax: RewriteBase A
Example: RewriteBase /~foo/bar/
Since: Apache 1.2
This directive explicitly sets the base URL for per-directory
rewriting. It is useful because RewriteRule can be used in
per-directory configuration files where it will act locally.
That is, the local directory prefix is stripped at this stage of
processing and your rewriting rules act only on the remainder.
The URL is added automatically at the end. Thus, when a
substitution occurs for a new URL, mod_rewrite reinjects the
URL into the server processing. To carry out this task, it needs
to know the corresponding URL prefix or URL base. By default,
the URL prefix is the corresponding file path itself. At most
web sites, however, URLs are not directly related to physical
file name paths, so this assumption will be usually be wrong!
In such a case, you must use the RewriteBase directive to
specify the correct URL prefix.