Perl 5.18 added vertical tab (or LINE TABULATION in the UCS) to the characters that match the
\s character class shortcut. It’s the one exception that made that shortcut different from the POSIX definition of whitespace. For the details, see my posts in The Effective Perler: The vertical tab is part of \s in Perl 5.18.
This means that a joke that I’ve used in almost 15 years of Perl teaching is going away. When I talked about
\s, I’d quiz the class on how much whitespace is in ASCII. Most people can name three immediately and four if they think for a moment. Many people forget about form feeds, and only two people in all of my classes have ever mentioned the vertical tab. However, it was only after I wrote about the vertical tab in Know your character classes under different semantics that a student mentioned it. I’m destroying my own lines for a class by writing about this stuff!