match_subdomains Inconsistency in Draft RFC?

Possible inconsistency in draft specifications.

I noticed that, in both the "draft-mengwong-spf-01.txt" from the IETF and
in the "spf-draft-200406.txt" on the website ( http://spf.pobox.com ),
there is a reference in section "2.2.2 Lookup" mentioning the use in SPF
records of "match_subdomains=yes", but in "Appendix A. Collected ABNF
for SPF records" that does not appear and would, if present in an SPF
record, apparently be interpreted as an "unknown-modifier"