Thanks for posting, I really like this series, even if I haven't used PHP much.
Often people have trouble adapting to a new language if they're really familiar with another one - the idioms, libraries and built ins are all so different, and it makes you realise a language is more than just a syntax, it's the culture, the libraries available etc.
Another area people might want isset is params coming in to a web endpoint, so yu might want to cover that in your examples.