title: Is optional or required the default for protocol methods?
body: <p>I used to think that the default/implicit specifier for protocol methods is optional. However, in my current project I see a warning if I do not add the @optional specifier specifically. Not a big deal. I am just wondering, was it optional the default for a while, and now it is required? Or maybe I missed something while I was learning Objective-C a while ago.</p>
  
  <p>Thanks in advance!</p>