case 'b':
		p.fmt.fmtInteger(v, 2, isSigned, verb, ldigits)
	case 'o', 'O':
		p.fmt.fmtInteger(v, 8, isSigned, verb, ldigits)
	case 'x':
		p.fmt.fmtInteger(v, 16, isSigned, verb, ldigits)
	case 'X':
		p.fmt.fmtInteger(v, 16, isSigned, verb, udigits)
	case 'c':
		p.fmt.fmtC(v)
	case 'q':
		p.fmt.fmtQc(v)
	case 'U':
		p.fmt.fmtUnicode(v)
	default:
		p.badVerb(verb)
	}
}

	\pF            Unicode character class F (one-letter name)

Named character classes as character class elements:

	[\d]           digits (== \d)
	[^\d]          not digits (== \D)
	[\D]           not digits (== \D)
	[^\D]          not not digits (== \d)
	[[:name:]]     named ASCII class inside character class (== [:name:])
	[^[:name:]]    named ASCII class inside negated character class (== [:^name:])

The first step divides n digits by n digits to ensure that it produces only a
single digit.

Each subsequent step appends the next digit from u to the remainder and divides
those n+1 digits by the n digits of v, producing another quotient digit and a
new n-digit remainder.

Subsequent steps divide n+1 digits by n digits, an operation that in general
might produce two digits. However, as used in the algorithm, that division is

//
// ```
// <quantity>        ::= <signedNumber><suffix>
//
// 	(Note that <suffix> may be empty, from the "" case in <decimalSI>.)
//
// <digit>           ::= 0 | 1 | ... | 9
// <digits>          ::= <digit> | <digit><digits>
// <number>          ::= <digits> | <digits>.<digits> | <digits>. | .<digits>
// <sign>            ::= "+" | "-"
// <signedNumber>    ::= <number> | <sign><number>

// as the second result value.
func formatBits(dst []byte, u uint64, base int, neg, append_ bool) (d []byte, s string) {
	if base < 2 || base > len(digits) {
		panic("strconv: illegal AppendInt/FormatInt base")
	}
	// 2 <= base && base <= len(digits)

	var a [64 + 1]byte // +1 for sign of 64bit value in base 2
	i := len(a)

	if neg {
		u = -u
	}

	// convert bits

			prec = digs.nd
		}
	} else if fmt != 'f' {
		// Fixed number of digits.
		digits := prec
		switch fmt {
		case 'e', 'E':
			digits++
		case 'g', 'G':
			if prec == 0 {
				prec = 1
			}
			digits = prec
		default:
			// Invalid mode.
			digits = 1
		}
		var buf [24]byte
		if bitSize == 32 && digits <= 9 {
			digs.d = buf[:]

func (s *ss) getBase(verb rune) (base int, digits string) {
	s.okVerb(verb, "bdoUxXv", "integer") // sets s.err
	base = 10
	digits = decimalDigits
	switch verb {
	case 'b':
		base = 2
		digits = binaryDigits
	case 'o':
		base = 8
		digits = octalDigits
	case 'x', 'X', 'U':
		base = 16
		digits = hexadecimalDigits
	}
	return
}

	`[:space:]`:   {+1, code14},
	`[:^space:]`:  {-1, code14},
	`[:upper:]`:   {+1, code15},
	`[:^upper:]`:  {-1, code15},
	`[:word:]`:    {+1, code16},
	`[:^word:]`:   {-1, code16},
	`[:xdigit:]`:  {+1, code17},
	`[:^xdigit:]`: {-1, code17},

		i = 2
		saw = '0' // base prefix counts as a digit for "underscore as digit separator"
		hex = lower(s[1]) == 'x'
	}

	// Number proper.
	for ; i < len(s); i++ {
		// Digits are always okay.
		if '0' <= s[i] && s[i] <= '9' || hex && 'a' <= lower(s[i]) && lower(s[i]) <= 'f' {
			saw = '0'
			continue
		}
		// Underscore must follow digit.
		if s[i] == '_' {
			if saw != '0' {
				return false

		case stdFracSecond0:
			// stdFracSecond0 requires the exact number of digits as specified in
			// the layout.
			ndigit := 1 + digitsLen(std)
			if len(value) < ndigit {
				err = errBad
				break
			}
			nsec, rangeErrString, err = parseNanoseconds(value, ndigit)
			value = value[ndigit:]

		case stdFracSecond9: