[tor-relays] a line "enable IPv6 on your relay"

hi, about that following lines in the mail from Moritz Bartl. [tor-relays] Please enable IPv6 on your relay!

In short, you add: ORPort [IPv6::address]:port IPv6Exit 1 ExitPolicy reject6 *:*

shouldnt there be a "a" in the first line? how important ist the letter a? i guess some operators just added the lines without "a" like above. additional: how many ipv6 relays are up NOW? and are there plans to include a button into torbrowser to enable/disable ipv6? thanks