What are potential pitfalls when using mod_rewrite with subdomains in PHP, and how can they be avoided?

Potential pitfalls when using mod_rewrite with subdomains in PHP include incorrectly configured rewrite rules that do not account for subdomains, leading to unexpected behavior or errors. To avoid this, ensure that the rewrite rules explicitly handle subdomains by using the %{HTTP_HOST} variable to capture the subdomain and properly redirect the request.

RewriteEngine On
RewriteCond %{HTTP_HOST} ^([a-zA-Z0-9-]+)\.example\.com$ [NC]
RewriteRule ^(.*)$ index.php?subdomain=%1 [QSA,L]