// if used in a URL.
//
// TODO(rsc): We would like to allow Unicode letters, but that requires additional
// care in the safe encoding (see "escaped paths" above).
func modPathOK(r rune) bool {
	if r < utf8.RuneSelf {
		return r == '-' || r == '.' || r == '_' || r == '~' ||
			'0' <= r && r <= '9' ||
			'A' <= r && r <= 'Z' ||
			'a' <= r && r <= 'z'
	}
	return false
}

// should only be given s. It's not curried for performance reasons.
func foldFunc(s []byte) func(s, t []byte) bool {
	nonLetter := false
	special := false // special letter
	for _, b := range s {
		if b >= utf8.RuneSelf {
			return bytes.EqualFold
		}
		upper := b & caseMask
		if upper < 'A' || upper > 'Z' {
			nonLetter = true
		} else if upper == 'K' || upper == 'S' {
			// See above for why these letters are special.

	last := 0
	for i := 0; i < len(b); i++ {
		c := b[i]

		if !jsIsSpecial(rune(c)) {
			// fast path: nothing to do
			continue
		}
		w.Write(b[last:i])

		if c < utf8.RuneSelf {
			// Quotes, slashes and angle brackets get quoted.
			// Control characters get written as \u00XX.
			switch c {
			case '\\':
				w.Write(jsBackslash)
			case '\'':
				w.Write(jsApos)
			case '"':

	case strings.EqualFold("iso-8859-1", charset):
		for _, c := range content {
			buf.WriteRune(rune(c))
		}
	case strings.EqualFold("us-ascii", charset):
		for _, c := range content {
			if c >= utf8.RuneSelf {
				buf.WriteRune(unicode.ReplacementChar)
			} else {
				buf.WriteByte(c)
			}
		}
	default:
		if d.CharsetReader == nil {
			return fmt.Errorf("mime: unhandled charset %q", charset)
		}

	// work, but it will not cause an allocation.
	if isASCII(v) {
		return v, nil
	}
	return idna.Lookup.ToASCII(v)
}

func isASCII(s string) bool {
	for i := 0; i < len(s); i++ {
		if s[i] >= utf8.RuneSelf {
			return false
		}
	}
	return true
}

// matcher represents the matching rule for a given value in the NO_PROXY list
type matcher interface {

		b.fill() // b.w-b.r < len(buf) => buffer is not full
	}
	b.lastRuneSize = -1
	if b.r == b.w {
		return 0, 0, b.readErr()
	}
	r, size = rune(b.buf[b.r]), 1
	if r >= utf8.RuneSelf {
		r, size = utf8.DecodeRune(b.buf[b.r:b.w])
	}
	b.r += size
	b.lastByte = int(b.buf[b.r-1])
	b.lastRuneSize = size
	return r, size, nil
}

func safeArg(name string) bool {
	if name == "" {
		return false
	}
	c := name[0]
	return '0' <= c && c <= '9' || 'A' <= c && c <= 'Z' || 'a' <= c && c <= 'z' || c == '.' || c == '_' || c == '/' || c >= utf8.RuneSelf
}

// parseGoEmbed parses the text following "//go:embed" to extract the glob patterns.
// It accepts unquoted space-separated patterns as well as double-quoted and back-quoted Go strings.

			Filename: name,
			Line:     1,
			Column:   1,
		},
	}
}

func isIdent(c byte) bool {
	return 'A' <= c && c <= 'Z' || 'a' <= c && c <= 'z' || '0' <= c && c <= '9' || c == '_' || c >= utf8.RuneSelf
}

var (
	errSyntax = errors.New("syntax error")
	errNUL    = errors.New("unexpected NUL in input")
)

// syntaxError records a syntax error, but only if an I/O error has not already been recorded.

			Filename: name,
			Line:     1,
			Column:   1,
		},
	}
}

func isIdent(c byte) bool {
	return 'A' <= c && c <= 'Z' || 'a' <= c && c <= 'z' || '0' <= c && c <= '9' || c == '_' || c >= utf8.RuneSelf
}

var (
	errSyntax = errors.New("syntax error")
	errNUL    = errors.New("unexpected NUL in input")
)

// syntaxError records a syntax error, but only if an I/O error has not already been recorded.

func (f *fmt) truncate(b []byte) []byte {
	if f.precPresent {
		n := f.prec
		for i := 0; i < len(b); {
			n--
			if n < 0 {
				return b[:i]
			}
			wid := 1
			if b[i] >= utf8.RuneSelf {
				_, wid = utf8.DecodeRune(b[i:])
			}
			i += wid
		}
	}
	return b
}

// fmtS formats a string.
func (f *fmt) fmtS(s string) {
	s = f.truncateString(s)
	f.padString(s)
}