Moodle 1.9.X only requires php 4. Moodle 2 requires php 5. http://docs.moodle.org/en/admin/environment/php

Support for access level keywords (public, protected, private) wasnt added until php 5. Thus the protected keyword shouldn't appear anywhere in moodle 1.9.X

There's at least one instance. grade/report/lib.php line 333. A quick search turned up a second instance in lib/simpletestlib/exceptions.php at line 118