Answer the context that called the receiver
Answer the MethodContext to which the receiver refers, or nil if it has been optimized away
Answer whether the receiver is a block context
Answers false, because contexts that are skipped when doing a return are always MethodContexts. BlockContexts are removed from the chain whenever a non-local return is done, while MethodContexts need to stay there in case there is a non-local return from the #ensure: block.
To create a valid execution environment for the interpreter even before it starts, GST creates a fake context whose selector is nil and which can be used as a marker for the current execution environment. Answer whether the receiver is that kind of context (always false, since those contexts are always MethodContexts).
Answers whether the context must continue execution even after a non-local return (a return from the enclosing method of a block, or a call to the #continue: method of ContextPart). Such contexts are created only by #ensure: and are always MethodContexts.
Answer the n-th outer block/method context for the receiver
Answer the outer block/method context for the receiver