5-0-3: Meaning of "implicitly converted to a different underlying type"

[misra cpp]

The purpose of the underlying type rules is to remove the dependency on 'usual arithmethic conversions' and other asymmetrical type behaviours defined in the standard, and to impose a uniform interpretation of arithmetic. Hence s64 = s32 + s32; is non-compliant by analogy with Example 1

According to the current rules, 0L == s32+s32 is compliant (0L is signed char, not a cvalue and can be converted to s32)