In one of my projects users are allowed to edit the same file. It is group work and max number of users in group is 4. It is rare that they will be editing at the same time but there is possibility of it. I am using ckeditor which displays the content. how I can lock the content while it is being edited? For the above case what will happen if one users open the content for editing and then never saves and leave window open. Is it possible to save the content, release the lock for editing by another users? If first user comes back to desk they should see the message that "content has been changed, please refresh".

I am using php, mysql.

Thanks