php manual location of class definition syntax?

I am having trouble with the online manual, finding section on class definition syntax. specifically, I am looking for where to place key words like 'extends' and 'final' I am working on a class that I don't want to allow extension. But when I place the key word final like so: class someClass final

         {
         }

I get a syntax error. I thought that was supposed to be the place to put those key words. So, my question is where is this addressed in the manual? All I have been able to find is classes/object information, which is a list of class/object related functions. Thanks for attention JK