vtable - C++ v-table: Part of the language or compiler dependent?

Question

Is the v-table (virtual method table) a part of the C++ specification, or is it up to the compiler to solve the virtual method lookups?

In case it's part of the spec: Why?

I'd guess that it's compiler dependent, but someone said to me that it's part of the spec.

References are very welcome!

Answer 1

1.7 The C++ memory model 3 [...] Various features of the language, such as references and virtual functions, might involve additional memory locations that are not accessible to programs but are managed by the implementation. [...]

There you have it. It is up to the implementation.