normal format spec, almost.
You can also say @samp{%6,4y}, which means that the field will never be
-more than 6 characters wide and never less than 4 characters wide.
+more than 4 characters wide and never less than 6 characters wide.
There are also specs for highlighting, and these are shared by all the
format variables. Text inside the @samp{%(} and @samp{%)} specifiers