Order of metatable accesses

["Joseph C. Sible" <josephcsible@...>]

Consider this Lua program:

local x = {
    a = setmetatable({}, {__newindex = function(t, k, v)
        print('setting a.' .. k)
    end}),
    b = setmetatable({}, {__newindex = function(t, k, v)
        print('setting b.' .. k)
    end}),
    c = setmetatable({}, {__index = function(t, k)
        print('getting c.' .. k)
    end}),
    d = setmetatable({}, {__index = function(t, k)
        print('getting d.' .. k)
    end})
}
setmetatable(_G, {__index = function(t, k)
    print('getting ' .. k)
    return x[k]
end})
a.foo, b.bar = c.baz, d.qux

When I run it, it prints this:

getting a
getting b
getting c
getting c.baz
getting d
getting d.qux
setting b.bar
setting a.foo

How much of the ordering of these metatable accesses is guaranteed? It
looks like it does all of the __index calls left-to-right and then all
of the __newindex calls right-to-left. But the only thing I see in the
manual is "The assignment statement first evaluates all its
expressions and only then the assignments are performed." Should the
manual make a stronger statement, or is what it says all that's
guaranteed and the other ordering I noticed just an implementation
detail?

Joseph C. Sible