Goal : In folders defined as "PUBLIC" for users in group "publicuser', any users can do anythings but cannot delete objects they do not own.  
1st Step :
 Creation of initial group, user and folders
Create group publicuser 
Create user publicuser (no login user), user_test1, user_test2 
 Add publicuser, user_test1, user_test2 to group publicuser
Create a new folder :     
 mkdir -p /d_pub_folder
 chown   publicuser:publicuser /d_pub_folder
Create sub-folder for each regular user    
 mkdir -p /d_pub_folder/user_test1
 chown user_test1:publicuser /d_pub_folder/user_test1
 mkdir -p /d_pub_folder/user_test2
 chown user_test2:publicuser /d_pub_folder/user_test2
Set properties on new folders    
 chmod -R 770 /d_pub_folder
 chmod -R g+s /d_pub_folder
 chmod -R +t  /d_pub_folder
Set ACL on new folders    
#set user to rwx, group to ---, group publicuser to rwx,other to ---    
 setfacl -R -m u::rwx,g::---,g:publicuser:rwx,o:---  /d_pub_folder
#set default : user to rwx, group to ---, group publicuser to rwx,other to ---    
 setfacl -R -d -m u::rwx,g::---,g:publicuser:rwx,o:---  /d_pub_folder
2nd Step :
Files creation Create new files owned by each user in their respective folder      
 su to user_test1
 echo "Create by user_test1 in user_test1's folder" > /d_pub_folder/user_test1/testfile_1.txt
 su to user_test2
 echo "Create by user_test2 in user_test2's folder" > /d_pub_folder/user_test2/testfile_2.txt
Create new files own by user_test2 in user_test1's folder      
 echo "Create by user_test2 in user_test1's folder" > /d_pub_folder/user_test1/testfile_4.txt
3rd Step : ACL Check from a "public" folder /d_pub_folder/....
 1°) OK : any user can create a file in it's own folder
 2°) OK : any user can create a file in folder owned by others
 3°) OK : any user can modify a file they owned in folder owned by others
 4°) OK : any user cannot delete a file they do not owned any where
 5°) OK : any user can modify a file they do not owned using vi in a terminal emulator (Konsole)
 What does not work :
  6°) FAILED : any user cannot modify a file they do not owned using KATE or KWRITE  in graphical session.