+ always print a sign for numeric values
- pad with spaces on the right rather than the left (left-justify the field)
# alternate format: add leading 0 for octal (%#o), 0x for hex (%#x);
- suppress 0x for %p (%#p);
+ 0X for hex (%#X); suppress 0x for %p (%#p);
print a raw (backquoted) string if possible for %q (%#q)
' ' (space) leave a space for elided sign in numbers (% d);
put spaces between bytes printing strings or slices in hex (% x)