What do you see in your pages at this point? Since you haven't set a custom include error message, you should see something like "include error" right in the body of the page for all to see. If you don't see the error, the file isn't even trying to do the includes. In that case you'll see the raw "<!--include et cetera" code when you look at the page source code.
:: wait ::
:: stop ::
:: rewind ::
Sorry. It's so obvious I overlooked it. In addition to AddOutputFilter you need
Options +Includes
or, for most sites,
Options -Indexes +Includes
--which reminds me that unless you have the worst host in the world, you should not need
IndexIgnore .htaccess
because a normal config file will already have rules about files with leading dot.
<!--#include file="includes/leftnav.html" -->
<!--#include virtual="/includes/leftnav.html" -->
It's a good thing your includes aren't working, or this would result in the same file being included twice. That's assuming the "includes" directory is in the same place as the file doing the including. (I checked in MAMP. I thought it would make an error but it simply included the same thing two times in a row.)
The Options +Includes line is unnecessary if the config file has includes enabled globally by default-- but this is very unlikely, since most people don't use them and it makes extra work for the server.
Edit: I had to go look up X-Bit Hack because I no longer use it. The htaccess/config directive is
XBitHack on
By itself, this does nothing. In the specific files that will be using includes, you need to set permissions to owner:execute. Exact mechanism depends on how you're accessing your files. In Fetch there's an Info window with a bunch of checkboxes. If you're doing it locally there's
:: ugh, ugh, shudder ::
a command-line equivalent. My notes say "chmod +x {drag file}". That's in
:: ugh, ugh, shudder ::
Terminal.
But if you plan on using includes everywhere in all directories, you don't need this. It's appropriate for situations where only a few files in a larger directory will have includes.