func (e DecoderError) Error() string {
	loc := fmt.Sprintf("%s [%d,%d]", quoteChar(e.atChar), e.pos[0], e.pos[1])
	s := fmt.Sprintf("%s %s: %s", e.msg, e.context, loc)
	if e.readerErr != nil {
		s += "\nreader error: " + e.readerErr.Error()
	}
	return s
}

// quoteChar formats c as a quoted character literal
func quoteChar(c byte) string {
	// special cases - different from quoted strings
	if c == '\'' {