static if(!(idx < 0))
static if(!(idx1 >= fmt.length - 1))
static if(!(fmt[idx2 + 1] == 's'))
static if(!(fmt[idx2 + 1] == 'c'))
static if(!(fmt[idx2 + 1] == 'b'))
static if(!(fmt[idx2 + 1].among('d', 'u')))
static if(!(fmt[idx2 + 1] == 'o'))
static if(fmt[idx2 + 1] == 'x')