I'm running Apache2 (2.0.43) and wanted to transparently send requests for
PHP-processed files to an Apache1.3 instance, which runs PHP Accelerator
(www.php-accelerator.co.uk). Naturally, I turned to mod_proxy and mod_rewrite.
However, I (think I've) found a problem with either the docs or with mod_rewrite
itself. Here's the ruleset I tried:

RewriteEngine on
RewriteCond %{REQUEST_FILENAME} \.php$
RewriteRule ^/+(.*)$ http://otherhost.horde.net/$1 [P,NE,L]

Turning on a RewriteLog showed that %{REQUEST_FILENAME} contained the URI of the
request, not the full local path as stated in the mod_rewrite docs
(http://httpd.apache.org/docs-2.0/mod/mod_rewrite.html). However, I found that
this ruleset works:

RewriteEngine on
RewriteCond %{LA-U:REQUEST_FILENAME} \.php$
RewriteRule ^/+(.*)$ http://otherhost.horde.net/$1 [P,NE,L]

In order to get the full local path in %{REQUEST_FILENAME}, you have to force
mod_rewrite to do a look-ahead with %{LA-U:REQUEST_FILENAME}.

The kicker is that the docs go on at length about the difference between
REQUEST_URI and REQUEST_FILENAME. I found these variables to be identical unless
you force mod_rewrite to look ahead for REQUEST_FILENAME. I posted to
apache-users, but didn't get any response after a few days and this doesn't seem
to be reported already. Is this a bug in the docs, mod_rewrite, or am I just
blowing hot air?