I don't know when examples are literal or placeholders.

This is slightly offtopic, but I just thought I might give some general advice. Most of the time, the things that are "placeholders" are either (1) variables or (2) strings. Exceptions should be pretty obvious, but if in doubt you can always simply play around with the example.

One thing to be careful of, though, is when you see the same "placeholder" used more than once. If there are two instances of $foo in a snippet, you can usually change them to whatever you want, but just make sure you change them both to the same thing. Hopefully this too is obvious, but sometimes what's obvious to one is not to another. =^)