[mxawng]

As fredemmott said above, we're hoping to build replacements for the various PHP builtins that we want to be a core part of Hack. I think that replacing the functionality provided by PHP builtins will be a less confusing transition experience than retrofitting them with modified behaviors would.

Once we do have a compelling and comprehensive Hack Standard Library, I wouldn't be surprised if we dropped PHP builtins in favor of that.