Questions regarding the "unbuffer" program (Expect)

/usr/bin/unbuffer has some constructs I'm not familiar with.  Observe:

1)  set stty_init "-echo"

What does this do?  "stty_init" isn't used anywhere else.  Is it some kind of
magic built-in variable?

2)  eval [list spawn -noecho] [lrange $argv 1 end]

Why use [list] here?  Whenever I've needed to do this, I just do:

    eval spawn -noecho [lrange $argv 1 end]

3)  close_on_eof -i $user_spawn_id 0

What is "close_on_eof"?  I've never heard of it and can't find it any of
the docs I checked.

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