func NewSmartypantsRenderer(flags HTMLFlags) *SPRenderer {
	var (
		r SPRenderer
		smartAmpAngled      = r.smartAmp(true, false)
		smartAmpAngledNBSP  = r.smartAmp(true, true)
		smartAmpRegular     = r.smartAmp(false, false)
		smartAmpRegularNBSP = r.smartAmp(false, true)
		addNBSP = flags&SmartypantsQuotesNBSP != 0
	)
	if flags&SmartypantsAngledQuotes == 0 {
		r.callbacks['"'] = r.smartDoubleQuote
		if !addNBSP {
			r.callbacks['&'] = smartAmpRegular
		} else {
			r.callbacks['&'] = smartAmpRegularNBSP
		}
	} else {
		r.callbacks['"'] = r.smartAngledDoubleQuote
		if !addNBSP {
			r.callbacks['&'] = smartAmpAngled
		} else {
			r.callbacks['&'] = smartAmpAngledNBSP
		}
	}
	r.callbacks['\''] = r.smartSingleQuote
	r.callbacks['('] = r.smartParens
	if flags&SmartypantsDashes != 0 {
		if flags&SmartypantsLatexDashes == 0 {
			r.callbacks['-'] = r.smartDash
		} else {
			r.callbacks['-'] = r.smartDashLatex
		}
	}
	r.callbacks['.'] = r.smartPeriod
	if flags&SmartypantsFractions == 0 {
		r.callbacks['1'] = r.smartNumber
		r.callbacks['3'] = r.smartNumber
	} else {
		for ch := '1'; ch <= '9'; ch++ {
			r.callbacks[ch] = r.smartNumberGeneric
		}
	}
	r.callbacks['<'] = r.smartLeftAngle
	r.callbacks['`'] = r.smartBacktick
	return &r
}
NewSmartypantsRenderer constructs a Smartypants renderer object.
package blackfriday
import (
	"bytes"
	"io"
)
type SPRenderer struct {
	inSingleQuote bool
	inDoubleQuote bool
	callbacks     [256]smartCallback
}
func wordBoundary(c byte) bool {
	return c == 0 || isspace(c) || ispunct(c)
}
func tolower(c byte) byte {
	if c >= 'A' && c <= 'Z' {
		return c - 'A' + 'a'
	}
	return c
}
func isdigit(c byte) bool {
	return c >= '0' && c <= '9'
}
func smartQuoteHelper(out *bytes.Buffer, previousChar byte, nextChar byte, quote byte, isOpen *bool, addNBSP bool) bool {
	switch {
	case previousChar == 0 && nextChar == 0:
		*isOpen = !*isOpen
	case isspace(previousChar) && nextChar == 0:
		*isOpen = true
	case ispunct(previousChar) && nextChar == 0:
		*isOpen = false
	case   nextChar == 0:
		*isOpen = false
	case previousChar == 0 && isspace(nextChar):
		*isOpen = false
	case isspace(previousChar) && isspace(nextChar):
		*isOpen = !*isOpen
	case ispunct(previousChar) && isspace(nextChar):
		*isOpen = false
	case   isspace(nextChar):
		*isOpen = false
	case previousChar == 0 && ispunct(nextChar):
		*isOpen = false
	case isspace(previousChar) && ispunct(nextChar):
		*isOpen = true
	case ispunct(previousChar) && ispunct(nextChar):
		*isOpen = !*isOpen
	case   ispunct(nextChar):
		*isOpen = false
	case previousChar == 0   :
		*isOpen = true
	case isspace(previousChar)   :
		*isOpen = true
	case ispunct(previousChar)   :
		*isOpen = true
	default:
		*isOpen = false
	}
	if addNBSP && !*isOpen {
		out.WriteString("&nbsp;")
	}
	out.WriteByte('&')
	if *isOpen {
		out.WriteByte('l')
	} else {
		out.WriteByte('r')
	}
	out.WriteByte(quote)
	out.WriteString("quo;")
	if addNBSP && *isOpen {
		out.WriteString("&nbsp;")
	}
	return true
}
func (r *SPRenderer) smartSingleQuote(out *bytes.Buffer, previousChar byte, text []byte) int {
	if len(text) >= 2 {
		t1 := tolower(text[1])
		if t1 == '\'' {
			nextChar := byte(0)
			if len(text) >= 3 {
				nextChar = text[2]
			}
			if smartQuoteHelper(out, previousChar, nextChar, 'd', &r.inDoubleQuote, false) {
				return 1
			}
		}
		if (t1 == 's' || t1 == 't' || t1 == 'm' || t1 == 'd') && (len(text) < 3 || wordBoundary(text[2])) {
			out.WriteString("&rsquo;")
			return 0
		}
		if len(text) >= 3 {
			t2 := tolower(text[2])
			if ((t1 == 'r' && t2 == 'e') || (t1 == 'l' && t2 == 'l') || (t1 == 'v' && t2 == 'e')) &&
				(len(text) < 4 || wordBoundary(text[3])) {
				out.WriteString("&rsquo;")
				return 0
			}
		}
	}
	nextChar := byte(0)
	if len(text) > 1 {
		nextChar = text[1]
	}
	if smartQuoteHelper(out, previousChar, nextChar, 's', &r.inSingleQuote, false) {
		return 0
	}
	out.WriteByte(text[0])
	return 0
}
func (r *SPRenderer) smartParens(out *bytes.Buffer, previousChar byte, text []byte) int {
	if len(text) >= 3 {
		t1 := tolower(text[1])
		t2 := tolower(text[2])
		if t1 == 'c' && t2 == ')' {
			out.WriteString("&copy;")
			return 2
		}
		if t1 == 'r' && t2 == ')' {
			out.WriteString("&reg;")
			return 2
		}
		if len(text) >= 4 && t1 == 't' && t2 == 'm' && text[3] == ')' {
			out.WriteString("&trade;")
			return 3
		}
	}
	out.WriteByte(text[0])
	return 0
}
func (r *SPRenderer) smartDash(out *bytes.Buffer, previousChar byte, text []byte) int {
	if len(text) >= 2 {
		if text[1] == '-' {
			out.WriteString("&mdash;")
			return 1
		}
		if wordBoundary(previousChar) && wordBoundary(text[1]) {
			out.WriteString("&ndash;")
			return 0
		}
	}
	out.WriteByte(text[0])
	return 0
}
func (r *SPRenderer) smartDashLatex(out *bytes.Buffer, previousChar byte, text []byte) int {
	if len(text) >= 3 && text[1] == '-' && text[2] == '-' {
		out.WriteString("&mdash;")
		return 2
	}
	if len(text) >= 2 && text[1] == '-' {
		out.WriteString("&ndash;")
		return 1
	}
	out.WriteByte(text[0])
	return 0
}
func (r *SPRenderer) smartAmpVariant(out *bytes.Buffer, previousChar byte, text []byte, quote byte, addNBSP bool) int {
	if bytes.HasPrefix(text, []byte("&quot;")) {
		nextChar := byte(0)
		if len(text) >= 7 {
			nextChar = text[6]
		}
		if smartQuoteHelper(out, previousChar, nextChar, quote, &r.inDoubleQuote, addNBSP) {
			return 5
		}
	}
	if bytes.HasPrefix(text, []byte("&#0;")) {
		return 3
	}
	out.WriteByte('&')
	return 0
}
func (r *SPRenderer) smartAmp(angledQuotes, addNBSP bool) func(*bytes.Buffer, byte, []byte) int {
	var quote byte = 'd'
	if angledQuotes {
		quote = 'a'
	}
	return func(out *bytes.Buffer, previousChar byte, text []byte) int {
		return r.smartAmpVariant(out, previousChar, text, quote, addNBSP)
	}
}
func (r *SPRenderer) smartPeriod(out *bytes.Buffer, previousChar byte, text []byte) int {
	if len(text) >= 3 && text[1] == '.' && text[2] == '.' {
		out.WriteString("&hellip;")
		return 2
	}
	if len(text) >= 5 && text[1] == ' ' && text[2] == '.' && text[3] == ' ' && text[4] == '.' {
		out.WriteString("&hellip;")
		return 4
	}
	out.WriteByte(text[0])
	return 0
}
func (r *SPRenderer) smartBacktick(out *bytes.Buffer, previousChar byte, text []byte) int {
	if len(text) >= 2 && text[1] == '`' {
		nextChar := byte(0)
		if len(text) >= 3 {
			nextChar = text[2]
		}
		if smartQuoteHelper(out, previousChar, nextChar, 'd', &r.inDoubleQuote, false) {
			return 1
		}
	}
	out.WriteByte(text[0])
	return 0
}
func (r *SPRenderer) smartNumberGeneric(out *bytes.Buffer, previousChar byte, text []byte) int {
	if wordBoundary(previousChar) && previousChar != '/' && len(text) >= 3 {
		numEnd := 0
		for len(text) > numEnd && isdigit(text[numEnd]) {
			numEnd++
		}
		if numEnd == 0 {
			out.WriteByte(text[0])
			return 0
		}
		denStart := numEnd + 1
		if len(text) > numEnd+3 && text[numEnd] == 0xe2 && text[numEnd+1] == 0x81 && text[numEnd+2] == 0x84 {
			denStart = numEnd + 3
		} else if len(text) < numEnd+2 || text[numEnd] != '/' {
			out.WriteByte(text[0])
			return 0
		}
		denEnd := denStart
		for len(text) > denEnd && isdigit(text[denEnd]) {
			denEnd++
		}
		if denEnd == denStart {
			out.WriteByte(text[0])
			return 0
		}
		if len(text) == denEnd || wordBoundary(text[denEnd]) && text[denEnd] != '/' {
			out.WriteString("<sup>")
			out.Write(text[:numEnd])
			out.WriteString("</sup>&frasl;<sub>")
			out.Write(text[denStart:denEnd])
			out.WriteString("</sub>")
			return denEnd - 1
		}
	}
	out.WriteByte(text[0])
	return 0
}
func (r *SPRenderer) smartNumber(out *bytes.Buffer, previousChar byte, text []byte) int {
	if wordBoundary(previousChar) && previousChar != '/' && len(text) >= 3 {
		if text[0] == '1' && text[1] == '/' && text[2] == '2' {
			if len(text) < 4 || wordBoundary(text[3]) && text[3] != '/' {
				out.WriteString("&frac12;")
				return 2
			}
		}
		if text[0] == '1' && text[1] == '/' && text[2] == '4' {
			if len(text) < 4 || wordBoundary(text[3]) && text[3] != '/' || (len(text) >= 5 && tolower(text[3]) == 't' && tolower(text[4]) == 'h') {
				out.WriteString("&frac14;")
				return 2
			}
		}
		if text[0] == '3' && text[1] == '/' && text[2] == '4' {
			if len(text) < 4 || wordBoundary(text[3]) && text[3] != '/' || (len(text) >= 6 && tolower(text[3]) == 't' && tolower(text[4]) == 'h' && tolower(text[5]) == 's') {
				out.WriteString("&frac34;")
				return 2
			}
		}
	}
	out.WriteByte(text[0])
	return 0
}
func (r *SPRenderer) smartDoubleQuoteVariant(out *bytes.Buffer, previousChar byte, text []byte, quote byte) int {
	nextChar := byte(0)
	if len(text) > 1 {
		nextChar = text[1]
	}
	if !smartQuoteHelper(out, previousChar, nextChar, quote, &r.inDoubleQuote, false) {
		out.WriteString("&quot;")
	}
	return 0
}
func (r *SPRenderer) smartDoubleQuote(out *bytes.Buffer, previousChar byte, text []byte) int {
	return r.smartDoubleQuoteVariant(out, previousChar, text, 'd')
}
func (r *SPRenderer) smartAngledDoubleQuote(out *bytes.Buffer, previousChar byte, text []byte) int {
	return r.smartDoubleQuoteVariant(out, previousChar, text, 'a')
}
func (r *SPRenderer) smartLeftAngle(out *bytes.Buffer, previousChar byte, text []byte) int {
	i := 0
	for i < len(text) && text[i] != '>' {
		i++
	}
	out.Write(text[:i+1])
	return i
}
type smartCallback func(out *bytes.Buffer, previousChar byte, text []byte) int