say outputs a trailing newline unless the arguments already contain a trailing newline.

Are you sure about that? The documentation makes no mention of such a condition and this example suggests that it is not the case:

D'oh! Of course, you are right, say simply appends a newline, and that's also what's written in the documentation.

The "add a newline unless there is already one" is my mental model of say, and my code never proved me wrong - because I never called it with a string already containing a trailing newline. And to make things worse, I even linked to the documentation in Re^5: Data::Dumper output. I wonder why my mental model of say is wrong. A blame on perlfunc states that the documentation hasn't changed for two years, and has no relevant changes since say was introduced.

Alexander