Let’s illustrate Forms mode with an example. Suppose you are looking at the /etc/passwd file, and the screen looks like this:
====== /etc/passwd ====== User : root Uid: 0 Gid: 1 Name : Super User Home : / Shell: /bin/sh
As you can see, the familiar fields from the entry for the super user are all there, but instead of being colon-separated on one single line, they make up a forms.
The contents of the forms consist of the contents of the fields of the record (e.g., ‘root’, ‘0’, ‘1’, ‘Super User’) interspersed with normal text (e.g., ‘User : ’, ‘Uid: ’).
If you modify the contents of the fields, Forms mode will analyze your changes and update the file appropriately. You cannot modify the interspersed explanatory text (unless you go to some trouble about it), because that is marked read-only (see Text Properties in The Emacs Lisp Reference Manual).
The Forms mode control file specifies the relationship between the format of /etc/passwd and what appears on the screen in Forms mode. See Control File Format.