The Emacs command M-x add-change-log-entry helps you keep a record of when and why you have changed a program. It assumes that you have a file in which you write a chronological sequence of entries describing individual changes. The default is to store the change entries in a file called ChangeLog in the same directory as the file you are editing. The same ChangeLog file therefore records changes for all the files in a directory.
A change log entry starts with a header line that contains your name and the current date. Except for these header lines, every line in the change log starts with a tab. One entry can describe several changes; each change starts with a line starting with a tab and a star. M-x add-change-log-entry visits the change log file and creates a new entry unless the most recent entry is for today’s date and your name. In either case, it adds a new line to start the description of another change just after the header line of the entry. When M-x add-change-log-entry is finished, all is prepared for you to edit in the description of what you changed and how. You must then save the change log file yourself.
The change log file is always visited in Indented Text mode, which means that LFD and auto-filling indent each new line like the previous line. This is convenient for entering the contents of an entry, which must be indented. See Text Mode.
Here is an example of the formatting conventions used in the change log for Emacs:
Wed Jun 26 19:29:32 1985 Richard M. Stallman (rms at mit-prep) * xdisp.c (try_window_id): If C-k is done at end of next-to-last line, this fn updates window_end_vpos and cannot leave window_end_pos nonnegative (it is zero, in fact). If display is preempted before lines are output, this is inconsistent. Fix by setting blank_end_of_window to nonzero. Tue Jun 25 05:25:33 1985 Richard M. Stallman (rms at mit-prep) * cmds.c (Fnewline): Call the auto fill hook if appropriate. * xdisp.c (try_window_id): If point is found by compute_motion after xp, record that permanently. If display_text_line sets point position wrong (case where line is killed, point is at eob and that line is not displayed), set it again in final compute_motion.