func (c *context) copy() bool {
	return c.writeBytes(c.src[c.pSrc : c.pSrc+c.sz])
}

// copyXOR copies the current rune to dst and modifies it by applying the XOR
// pattern of the case info. It is the responsibility of the caller to ensure
// that this is a rune with a XOR pattern defined.
func (c *context) copyXOR() bool {
	if !c.copy() {
		return false
	}
	if c.info&xorIndexBit == 0 {