Re: [PHP-DEV] Class Extension

> There is no such check in PHP. Static Analysis tools may warn about it, but a trait will compile fine with code that refers to unknown members. The code will then succeed or fail at runtime just like any other object access:

I have to admit I never knew that worked. I genuinely learned something new today. 

Now knowing that, it makes the case for using a different keyword like `extension` much stronger since that is not the case for an extension. Everything on an extension is type-checked at compile time, save some edge cases with scalars.