It's from the System V Interface Definition standard. See page 625 in http://www.sco.com/developers/devspecs/vol1a.pdf http://www.sco.com/developers/devspecs/v

It's from the System V Interface Definition standard. See page 625 in http://www.sco.com/developers/devspecs/vol1a.pdf http://www.sco.com/developers/devspecs/vol1a.pdf > During input, erase and kill processing is normally done. The ERASE character (by default, the # character) erases the last character typed. The WERASE character (CRTL-W) erases the last ‘‘word’’ typed in the current input line (but not any preceding spaces or tabs). A ‘‘word’’ is defined as a sequence of non-blank characters, with tabs counted as blanks. Neither ERASE nor WERASE will erase beyond the beginning of the line. The KILL character (by default, the @ character) kills (deletes) the entire input line, and optionally outputs a newline character. All these characters operate on a key stroke basis, independent of any backspacing or tabbing that may have been done. The REPRINT character (CTRL-R) prints a newline followed by all characters that have not been read. Reprinting also occurs automatically if characters that would normally be erased from the screen are fouled by program output. The characters are reprinted as if they were being echoed; consequencely, if ECHO is not set, they are not printed.