In my own words, after reading the docs and experimenting:
You can use RewriteBase
to provide a base for your rewrites. Consider this
# invoke rewrite engine RewriteEngine On RewriteBase /~new/ # add trailing slash if missing rewriteRule ^(([a-z0-9\-]+/)*[a-z0-9\-]+)$ $1/ [NC,R=301,L]
This is a real rule I used to ensure that URLs have a trailing slash. This will convert
http://www.example.com/~new/page
to
http://www.example.com/~new/page/
By having the RewriteBase
there, you make the relative path come off the RewriteBase
parameter.