> A character is "graphic" if it takes up room on the display surface: thus a
> letter, number, punctuation mark, symbol, combining character (none in
> ASCII), or any of Unicode's various space separator characters.  It is
> "printable" if it also leaves ink on the display surface, which excludes
> the last group.  (Unicode does not define "printable", but ISO C and C++
> do.)

Based on BSD manual pages, isprint() is like isgraph() but also includes
the space character. isprint() does not include tab or newline.