A valid variable name starts with a letter or underscore, followed by any number of letters, numbers, or underscores. As a regular expression, it would be expressed thus: '[a-zA-Z_x7f-xff][a-zA-Z0-9_x7f-xff]*'

Technically, you can get around this in two different ways - variable varaibles and the more complex notation with curly braces. He points to the compact function for proof that they're set.

I just noticed today, that PHP's try catch blocks require curly braces. Anybody has an idea why it is like that? I have used curly braces by default up until now, so I just stumbled upon this weirdness today.

He includes two examples, one with a curly brace after the catch clause and the other without. This is different than several other control structures (like ifs) that don't require the curly brace when there's only the one line following it.