[exim] typo in Ch 37, dovecot authenticator?

http://www.exim.org/exim-html-current/doc/html/spec_html/ch37.html

The text says "the identity of the user who authenticated is placed in
$auth1", but the example show use of both "$auth1" and "$auth2".

Does someone know offhand which is correct (to save my lazy self from
finding out experimentally)?

TIA!