A Char accepting output range.
A std.format.FormatSpec which controls how this is formatted.
toString is rarely directly invoked; the usual way of using it is via std.format.format:
import std.format; assert(format("%04d", checked(15)) == "0015"); assert(format("0x%02x", checked(15)) == "0x0f");
Writes a string representation of this to a sink.