fmt.Printf("%d", BoolFormatter(true))       // ERROR "Printf format %d has arg BoolFormatter\(true\) of wrong type .*print.BoolFormatter"
	fmt.Printf("%z", FormatterVal(true))        // correct (the type is responsible for formatting)
	fmt.Printf("%d", FormatterVal(true))        // correct (the type is responsible for formatting)
	fmt.Printf("%s", nonemptyinterface)         // correct (the type is responsible for formatting)