Pointing parked domain to a sub-directory

Issue :

How to point a parked domain to a sub-directory of the main domain without any change in the URL ?

Fix :

This is like making the parked domain function like an add-on domain.
Assuming that the parked domain name is abc.com and the corresponding folder under the main domain is ‘abc’ .This can be achieved by putting the following in the .htaccess file for the main domain :

RewriteEngine On
Options +FollowSymlinks
RewriteBase /
RewriteCond %{HTTP_HOST} abc.com
RewriteCond %{REQUEST_URI} !abc/
RewriteRule ^(.*)$ abc/$1 [L]