What happens if allowance goes negative?

[0xgizmob]

From the transferFrom method, the line 235

if (allowed != type(uint256).max) {
        allowance[from_][msg.sender] = allowed - value;
      }

Should there be a check to ensure value < allowed, and revert if so?

[caldereth]

This will already revert due to underflow, so no need to explicitly check.