Set the KeyAttr option for <nonterminal> to the empty list.

See XML::Simple for further details.

Update: quick explanation for my rather terse answer... when elements are repeated, XML::Simple puts them into either a hash or an array. It chooses a hash if it can find an attribute to use as the hash key. By default the attributes id, key and name are used. Perl hashes don't preserve order; Perl arrays do. By setting the key attribute list to the empty list, you force XML::Simple to use arrays.

That having all been said, in my experience for any even vaguely complex tasks, XML::Simple's "simplicity" actually ends up making things much harder. Witness the XML::LibXML solution...

use 5.010;
use XML::LibXML 1.94;
use PerlX::MethodCallWithBlock;

XML::LibXML::
    -> load_xml(location => 'myfile.xml')
    -> findnodes("//nonterminal | //token")
    -> map { $_->{name} || $_->textContent }
    -> foreach { say }
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