publickey subsystem?

[Mouse <mouse%Rodents-Montreal.ORG@localhost>]

http://www.php.net/manual/en/function.ssh2-publickey-init.php, as
linked to by http://php.net/manual/en/book.ssh2.php, indicates that
there exists a `publickey' subsystem, which provides
implementation-agnostic editing of authorized-keys files.

I don't recall seeing this mentioned before, though it's certainly
possible this says more about my memory than it does about what I've
actually seen go by.  But, in any case, I'd like to find a spec for
that subsystem, so I can at least consider implementing it for moussh.
Anyone know if there's a spec available?  RFC, I-D, whatever?

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