Any extensions marked as IFormatter.CanAutoDetect will be called implicitly
(when no formatter name is specified in the input format string).
For example, "{0:N2}" will implicitly call extensions marked as IFormatter.CanAutoDetect.
Implicit formatter invocations should not throw exceptions.
With IFormatter.CanAutoDetect == false, the formatter can only be
called by its name in the input format string.
If more than one registered IFormatter can auto-detect, the first one in the formatter list will win.