When did the file mode in Perl's open become a separate argument?

Question

Once upon a time, you opened files in Perl like so:

open(FH, ">$filename");

At some point, for many good reasons including some very sticky ones involving filenames with leading spaces, this syntax became available (and, immediately, preferred):

open(FH, '>', $filename);

What version of Perl did we get that syntax with?

Answer 1

Looks like 5.6.0.