From type/IO/Handle

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method print-nl(IO::Handle:D: --> True)

Writes the value of $.nl-out attribute into the handle. This attribute, by default, is ␤, but see the page on newline for the rules it follows in different platforms and environments.

Attempting to call this method when the handle is :$enc will result in X::IO::BinaryMode exception being thrown.

my $fh = 'path/to/file'.IO.open: :w, :nl-out("\r\n");
$fh.print: "some text";
$fh.print-nl; # prints \r\n 
$fh.close;

From type/IO/CatHandle

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multi method print-nl(|)

The IO::CatHandle type overrides this method to throw a X::NYI exception. If you have a good idea for how this method should behave, tell Rakudo developers about it!