This page is part of the web mail archives of SRFI 52 from before July 7th, 2015. The new archives for SRFI 52 contain all messages, not just those from before July 7th, 2015.
I just noted that Tab, Form Feed, Line Feed, and Carriage Return have Unicode class Cc [Control Code] and are not in Zs (Separator, space) or Zl (Separator, line). I suspect the char-whitespace? definition should include them. Cheers, -KenD