Don't work together.
I think it's a bug in mod_rewrite, to be honest, though more of a "not thinking these two modules would ever be used together" kind of oversight, rather than a full bug.
Essentially, if you are using MultiViews to make for pretty URLs (say, http://www.foo.com/bar, where 'bar' doesn't exist, but instead loads the content from bar.php), and you attempt to implement RewriteRules to modify the URL, you will see erratic results.
If, for example, you have a RewriteRule as follows:
RewriteCond %{HTTP_HOST} !^www\.foo\.com
RewriteRule (.*) http://www.foo.com/$1 [R=301,L]
which, essentially, takes all non-WWW requests and makes them www.foo.com, you will find that MultiView URLs will be redirected to their real resources if the URL matches a rule. For example,
http://foo.com/bar
will become
http://www.foo.com/bar.php
after going through the MultiView filter and the RewriteRules. This is due to the way the rules work — essentially, the request will be parsed through mod_rewrite to find a match. If no match against the URL, the MultiView is processed to get the real resource which is then presented to the end user. If a match is made, however, mod_rewrite has mod_negotiation process the MultiView to find the real resource so it can properly do the rewrite — it is never changed back, however, to the pretty MultiView URL. If your goal is pretty URLs without any effort expended, relying on MultiView, you will find that RewriteRules are your nemesis.
There are a few routes available to get around this odd behavior, but my favorite (and easiest to implement) is to move the RewriteRule logic to the site code. It's much harder to implement MultiView-esque functionality than it is to re-implement RewriteRules.
To implement the above RewriteRule, redirecting non-www to www, simply add an auto_prepend_file to your .htaccess in lieu of the RewriteRule as such:
php_value auto_prepend_file "/var/www/html/prepend.php"
This file contains simply:
<?
if ( !
( preg_match('/^www/',
$_SERVER['SERVER_NAME']) ) ) {
header("Location: http://www.$_SERVER[SERVER_NAME]$_SERVER[REQUEST_URI]");
}
?>
With this code prepended to every PHP script (assuming your site is written in PHP, of course), all non-www requests will be redirected to www — *after* the MultiView is processed and not interfering with its inner workings.