Thanks for the responses guys! I get it now. Actually, it's kind of clever:
. + ' => !
I think I read somewhere that some old typewriters saved key space by using that eliminating the exclamation point and forcing typists to use that combo.
Still, it seems kind of hard for me to scan it as two separate components: my brain parses "foo!bar" quite differently than "foo.bar" - I guess it'll become more natural with time.
As the next installment in our "A confession of stupidity" series [1], I never realized that before. :) Turns out that superimposing chars on top of each other to make other chars is an addictive game, though. Here are a few I came up with:
|S => $
:, => ;
++++ or //= => #
o/o => %
ao or aO => @
\S => &
-x or -X => *
|_ => L
/-\ => A
|3 => B
][ => I
|-| => H
C- => G
|= => F
|^^| => M or m
|< => K
|? or |> => P
|o => b
|) => D
-/_ => z
O, => Q
-| => +
|\| => N
bP => B
Unfortunately, few if any of these could be useful for Arc.