- character with strictly positive width, which must be
- the first, and contain no characters of negative
- width.
+ spacing character, which must be the first.
+
+ Up to <STRONG>CCHARW_MAX</STRONG>-1 nonspacing characters may follow.
+ Additional nonspacing characters are ignored.
+
+ The string may contain a single control character
+ instead. In that case, no nonspacing characters are
+ allowed.