How to open temporary with Perl 5.6?

Hi,

in the test suite of one of my modules I use

open TMP, '+>', undef or die ...

to open a temporary file which is more or less as it is documented in
my Perl 5.8.8 documentation:

> As a special case the 3-arg form with a read/write mode and the
> third argument being "undef":
>
> open(TMP, "+>", undef) or die ...
>
> opens a filehandle to an anonymous temporary file.

Now I received my first test error from the CPAN testers for that
statement:
> Use of uninitialized value in open at t/Parse-Readelf.t line 45.

The tester runs Perl 5.6.2, so I suppose the temporary functionality
was added later. Now my questions would be:
Which Perl version added the special temporary syntax?
Is there some other portable easy-to-use construct to open a temporary
file with Perl versions 5.6.1 or later?

Regards, Thomas
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