Notepad ++ and regex

I am doing some tests with Find in Notepad ++ using regex. Here is my problem that I cannot figure out why:

My text:

abc/xyz/p234/s-sdf

      

        
        
        
      

    

The following regex matches well:

[a-z]+/[a-z]+(/p[0-9]+)/s-[a-z]+

      

        
        
        
      

    

But why does the following regex (with "?" Appended) no longer match:

[a-z]+/[a-z]+(/p[0-9]+)?/s-[a-z]+

      

        
        
        
      

    

Am I correct that in the last regex '?' means that (/ p [0-9] +) can be displayed zero or one time?