Well this video
http://www.youtube.com/watch?v=3mw0jLNVFp0 answers but now when that special user adds a file/image to a document the path to that file is not correct...
I gave the directory /assets/webmaster/ to that user and I created a directory images into it
and when that user adds an image, the image path is /images/example.gif and it should be /assets/webmaster/images/example.gif
What could I do to fix that?