[ashleyn]

This doesn't seem too odd to me when considering it may be a convention of writing a lexer. E.g. symbols defined not just one-to-one with ASCII characters, but may also include something like DOUBLE_EQUALS, STRING_LITERAL, NUMBER_LITERAL, etc.

[Macha]

And in fact...

    define('ISEMAIL_STRING_DOUBLECOLON' , '::');
    define('ISEMAIL_STRING_IPV6TAG'  , 'IPv6:');