colon pair confusion

Hi All,

I am a bit confused as to what colon pairs are actually doing:

[0] > my $y=:abc;
abc => True
Why is this True and not Nil?


[1] > my $y=:abc(123);
abc => 123
This I get.


[2] > my $y=:abc();
abc => ()
Why is this () and not Nil?


[3] > my $y=:abc(Nil);
abc => Nil
This I get


Yours in Confusion,
-T