First, prefer the leaner "parent" module over the heavy "base"
module to establish ISA relationships, since "base" is only
needed for "fields".
The "//" and "//=" operators allow us simplify our code and fix
minor bugs where a value of "0" was disallowed. Yes, we'll
allow "0" as an email address, too, since some twisted BOFH
could theoretically use it as a local user name.
Going forward, we'll also be avoiding "use warnings" and
instead rely on `-w' in the shebang.