respecting the `auto` settings of the former if we are going to a
terminal). `auto` alone (i.e. `%C(auto)`) will turn on auto coloring
on the next placeholders until the color is switched again.
-- '%m': left, right or boundary mark
+- '%m': left (`<`), right (`>`) or boundary (`-`) mark
- '%n': newline
- '%%': a raw '%'
- '%x00': print a byte from a hex code