All text after one $ or between two $ signs on one line in the command file is ignored by SWAN as comment. Such comments may be important to the user e.g., to clarify the meaning of the commands used. In fact, this option has been used to create the edit file swan.edt (see Appendix C). Anything appearing after two $ signs is not interpreted as comment, but again as data to be processed (possibly interrupted again by $ or two $ signs). Since version 40.20, the exclamation mark `!' can be used as comment sign. Everthing behind a ! is interpreted as comment, also if ! or $ are in that part of the input line.