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

[tor-server-creator at use.startmail.com]

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
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