If abc.com is your original domain and xyz.com is the domain alias, and
you want people going to abc.com to see one site and people going to
xyz.com to see a different site, and you want the hostname to stay as
the user typed it, make a directory called xyz under /htdocs/www and put
the xyz.com website in it. Then use mod_rewrite in an .htaccess file in
/htdocs/www
Code:
RewriteEngine On
RewriteCond %{HTTP_HOST} xyz.com$ [NC]
RewriteCond %{REQUEST_URI} !^/xyz/.*$
RewriteRule ^(.*)$ /xyz/$1
Now when people go to abc.com they will see the site in /htdocs/www.
When people go to xyz.com, they will be served pages from
/htdocs/www/xyz and the URL in their browser will not change the
hostname or show them the /xyz/.