Example:
A directory "files" contains the file "text", with the following rights:
drwxr-xr-x 1 root bin 4 21 May 10:43 files/
|
+--> -rwxr-xr-x 1 bob users 240 26 Jun 03:47 text
User "bob" can modify the file "text" in the "files" directory, but he can not delete it: file creation and deletion are submitted to the access right of the directory the file is created / deleted in.