That is the same with any language. An expert should not only know the language as defined by the standard or canonical implementation, but also the majority of implementations for the said language and consequent deviations from the official language semantics.

Ergo, no one is actually a real expert in a specific language.

Kay is an expert in Smalltalk and Wirth is an expert in Oberon.

Stroustrup is an expert at nailing legs to a dog and calling it an octopus.

> Kay is an expert in Smalltalk and Wirth is an expert in Oberon.

No, they are experts on the implementations they created, not on the other ones that were created.

That standard is too arbitrary and stringent.

I wonder how's salary comparing to other programming languages?