For example, the below code would display different code depending on if the request for the page was made via AJAX or directly via a browser.

if(isset($_SERVER['HTTP_X_REQUESTED_WITH']) && strtolower($_SERVER['HTTP_X_REQUESTED_WITH']) == 'xmlhttprequest') {
    //This is an AJAX request, do AJAX specific stuff
}
else {
    //This is not an AJAX request E.g. display normal page content.
}

In some code I was working on today, I saw a neater way of achieving the above, this would be included in your common config file:

define('IS_AJAX_REQUEST', isset($_SERVER['HTTP_X_REQUESTED_WITH']) && strtolower($_SERVER['HTTP_X_REQUESTED_WITH']) == 'xmlhttprequest');

if(IS_AJAX_REQUEST) {
    //This is an AJAX request, do AJAX specific stuff
}
else {
    //This is not an AJAX request E.g. display normal page content.
}

There’s an HTTP variable set called HTTP_X_REQUESTED_WITH, which will is set to ‘XMLHttpRequest‘ if the request method is via AJAX. This is method is untested with JavaScript frameworks other than JQuery, so may not work (but I don’t see any reason at all why it wouldn’t!).

It’s also worth noting that not all web servers include this variable and sometimes omit this specific $_SERVER paramter. Use vardump($_SERVER) to check that the HTTP_X_REQUESTED_WITH is present.

RewriteBase /
RewriteEngine on
RewriteRule amnesia/resetpass(.*) recover-password.php$1 [PT]

So typing in www.domain.com/amnesia/resetpass does a simple re-write to www.domain.com/recover-password.php, without the user ever knowing. All is fine. However, when I treid to get this seemingly simple rule to work with XAMPP I ran into problems, getting 404 and 500 responses from the server – obviously quite a pain as this essentially means I can’t test the site using my own web server (E.g. localhost). The site hosted from my computer via the normal setup E.g. xampp/htdocs/mysite. I’ll jump straight to the solution and then explain exactly what things were changed – the working htaccess file is below:

RewriteEngine on
RewriteBase /mysite
options +FollowSymLinks
RewriteRule amnesia/resetpass(.*) recover-password.php$1 [PT]

Firstly, the extra line that uses the +FollowSymLinks directive was added. To explain this I’ll quote straught from the Apache documentation:

To enable the rewriting engine for per-directory configuration files, you need to set “RewriteEngine On” in these files and “Options FollowSymLinks” must be enabled. If your administrator has disabled override of FollowSymLinks for a user’s directory, then you cannot use the rewriting engine. This restriction is needed for security reasons.

The re-write base has been changed to the relative path of the website directory. To finish up, open the http.conf file (the default settings for XAMPP, that get overwritten with you .htaccess file rules on a directory basis), located by default at C:\xampp\apache\conf\http.conf. Find all occurances of AllowOverride None and change it to AllowOverride All. After restarting XAMPP everythign should work. In a nutshell changing the AllowOverride directive in the http.conf file decalres which directives in .htaccess files can override directives from httpd.conf, this is discussed in more dept over here, but basically by having this directive set to None, you’re stopping individual htaccess files from working locally.