There's no python standard, but my guess is that-- since this is based on the same source code that native PyPy is, with a different compiler backend -- they a

There's no python standard, but my guess is that-- since this is based on the same source code that native PyPy is, with a different compiler backend -- they are making the claim based on the fact that native PyPy is widely considered to be similar enough to CPython for many workloads. Thus -- assuming the correctness of the RPython -> JavaScript transformation (which they have not proven, and would be a monumental task) -- you should expect this version to work like the native PyPy.