behaviour of STDOUT and STDERR

thiagu_mvt has asked for the wisdom of the Perl Monks concerning the following question:

print STDOUT "Output with Newline\n\n      between";
print STDERR "FirstLine\nSecondLine\nThirdLine";
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when executed it prints

[host1]$ perl out_err.pl
Output with Newline

FirstLine
SecondLine
ThirdLine      between
[download]

Why is contents of stdout printed after stderr ? because each stdout and stderr are launched in different threads and stderr finished soon ?
can somebody explain accurately ?
-Thiagu

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