The spec uses the word "expected" several times, and, as the discussion in #732 shows, the meaning of this word is not quite clear. I would propose to make it clear that these expectations are actually requirements, and reword accordingly.

Specifically, in the definition of the Integer type, change

64 bit (signed long) range expected

to

TOML implementations must be able to losslessly handle at least all
integers in the 64 bit (signed long) range

In the sections on time-related types, change

The precision of fractional seconds is implementation-specific, but at least
millisecond precision is expected.

to

The precision of fractional seconds is implementation-specific, but TOML
implementations must support at least millisecond precision.

(This change needs to be done three times, in the sections on Offset Date-Time, Local Date-Time, and Local Time).

The first wording has been moved out of #732 because the issue has turned out to be controversial. So let's discuss it here!