return r == '_' || unicode.IsLetter(r) || unicode.IsDigit(r)
}

func hasLeftTrimMarker(s string) bool {
	return len(s) >= 2 && s[0] == trimMarker && isSpace(rune(s[1]))
}

func hasRightTrimMarker(s string) bool {
	return len(s) >= 2 && isSpace(rune(s[0])) && s[1] == trimMarker

	rst7Marker = 0xd7 // ReSTart (7).
	soiMarker  = 0xd8 // Start Of Image.
	eoiMarker  = 0xd9 // End Of Image.
	sosMarker  = 0xda // Start Of Scan.
	dqtMarker  = 0xdb // Define Quantization Table.
	driMarker  = 0xdd // Define Restart Interval.
	comMarker  = 0xfe // COMment.
	// "APPlication specific" markers aren't part of the JPEG spec per se,
	// but in practice, their use is described at