Understanding uniqueness of selectors in Objective-C

Question

I am having problem understanding part of the function of \"selectors\", as described in Apple\'s guide. I\'ve bolded the parts where I am getting confused:

Answer 1

Look at the SEL type, you don't have to define which class this selector is from, you just give it a method name, for example:

SEL animationSelector = @selector(addAnimation:forKey:); 

You can imagine it as a streetname, for example. Many cities can have the same streetnames, but a streetname without a city is worthless. Same for selectors, you can define a selector without adding the object where it's in. But it's complete worthless without fitting class..