A link to the latest MPE spec is available in the "Supplemental Specifications [after 1996]" section on this page.

The latest I found is 2 years old: https://docs.google.com/document/d/1vpjxoPHw82X3xyNvE6_hsDeL86vloNQZC83NHD8edow
I wonder if there is any more recent version...

According to this web site, this spec has JUST been agreed, and the spec has not yet been published.

When it IS published, the full spec will be available on this site.

I would assume it will be added to the 'SPEC' section.

Geoff