ASCII characters to indicate carriage return or tab or backspace; typed by depressing a key and the control key at the same time. When a user mistypes, the Backspace key undoes the erroneous characters. 表示回车、退格或制表的ASCII字符;同时按住一个键和control键可以打出来。当用户输入错误时,可以按退格键撤销错误的字符。