trn valid_message_id() rejects valid message ids

[Eamonn McManus]

0004475895 at mcimail.com writes:
>> [trn] considers invalid any id whose local part contains any lower case
>> letter and no digits.
>
>This should read "...no upper case letters or digits."

I would like to know how the code I quoted could be interpreted this way.

,
Eamonn