Why are nested records of type metatable<T>, while top-level records are not?

[parke]

Why are nested records of type metatable<T>, while top-level records are not?

Is this behavior (and the rationale behind it) documented somewhere?

Thanks!

Here is an example.

[ UPDATE: I guess this example is not particularly practical or useful. In order to be useful, the record's table (for example: C.D) needs to be set to the __index field of a separate metatable table. However, the example still does expose curious and unexpected behavior by the compiler. ]

global record  A  end

local  record  B  end

local  record  C
  record  D  end
end

setmetatable ( {} as A, A )
--  The above line causes a compile time error.  But why?                       
--    argument 2: A is not a metatable<T>                                       

setmetatable ( {} as B, B )
--  The above line causes a compile time error.  But why?                       
--    argument 2: B is not a metatable<T>                                       

setmetatable ( {} as C, C )
--  The above line causes a compile time error.  But why?                       
--    argument 2: C is not a metatable<T>                                       

setmetatable ( {} as C.D, C.D )
--  The above line compiles successfully without any error.                     

print  'Success.'

Here is what happens when I try to tl run the above code.

$ tl run test.tl
========================================
3 errors:
test.tl:10:25: argument 2: A is not a metatable<T>
test.tl:14:25: argument 2: B is not a metatable<T>
test.tl:18:25: argument 2: C is not a metatable<T>
----------------------------------------
3 errors

[parke]

The below code is also interesting. I would expect that the Teal compiler would detect the type mismatch and generate a compile time error. But the code compiles and runs successfully.

local  record  C
  record  D  end
  record  E  end
end

setmetatable ( {} as C.D, C.D )
--  The above line compiles successfully (as expected) without any error.

setmetatable ( {} as C.D, C.E )
--  The above line unexpectedly(!) compiles successfully.
--  I would expect a compile time error.

print  ''
print  'Success.'