awk limitation, probably to be documented in the autoconf manual?

Hi autoconf maintainers,

the sections "Limitations of Shell Builtins" and "[Limitations of Usual Tools" of the Autoconf manual have the status as a reference for portable shell programming for me.

So how about the following limitation of "awk" related to arrays used in functions:

---- test program ----
function foo( bar )
{
  for ( x in bar ) print "foobar";
}

END { foo(); }
---- test program ----

When executing this as "cat /dev/null | <awk> -f <test program>" I get on the test systems I have access to:

------------------------------
AIX host 2 7 00F7BD2A4C00
nawk
awk:  must be an array.

 The source line number is 3.
------------------------------
HP-UX host B.11.31 U 9000/800 531545342 unlimited-user license
awk
awk:  must be an array.
 The source line number is 3.
------------------------------
HP-UX host B.11.31 U ia64 3184477447 unlimited-user license
awk
awk:  must be an array.
 The source line number is 3.
------------------------------
SunOS host 5.10 Generic_Virtual sun4v sparc sun4v
nawk
nawk: (null) is not an array
 source line number 3
------------------------------
SunOS host 5.10 Generic_141445-09 i86pc i386 i86pc
nawk
Segmentation Fault - core dumped
------------------------------

Only the GNU "gawk" on GNU/Linux groks that example.

Of course, that use of a local variable as an array may be non-POSIX-ish.  Haven't found anything on that.

Thanks for maintaining autoconf!

Jens