code: func lexString(l *lexer) stateFn {
  Loop:
  	for {
  		switch l.next() {
  		case '\\':
  			lexEscape(l)
  		case utf8.RuneError:
  			return l.errorf("invalid UTF-8 rune")
  		case eof, '\n':
  			return l.errorf("unterminated quoted string")
  		case l.stringOpen:
  			break Loop
  		}
  	}
  	l.emit(ItemString)
  	return lexStatements
  }
docs: // lexString scans a quoted string. The initial quote has already been seen.