$Email::Address::addr_spec
    This regular expression defined what an email address is allowed to
    look like.

$Email::Address::angle_addr
    This regular expression defines an $addr_spec wrapped in angle
    brackets.

$Email::Address::name_addr
    This regular expression defines what an email address can look like
    with an optional preceeding display name, also known as the
    "phrase".

$Email::Address::mailbox
    This is the complete regular expression defining an RFC 2822 emial
    address with an optional preceeding display name and optional
    following comment.