Things useful to do for GNU Emacs:

* Primitive for random access insertion of part of a file.

* Making I/O streams for files, so that read and prin1 can
 be used on files directly.  The I/O stream itself would
 serve as a function to read or write one character.

* Can gc compactify strings in place rather than copying all
 of string space?  Current technique of copying is vulnerable
 to a fatal error if copying strings exhausts memory during gc.

 Alternatively, be able to use secondary storage for copying
 strings if run out of memory for doing so.

* If a file you can't write is in a directory you can write,
 make sure it works to modify and save this file.

* Make dired's commands handle correctly the case where
 ls has listed several subdirectories' contents.
 It needs to be able to tell which directory each file
 is really in, by searching backward for the line
 which identifies the start of a directory.

* Add more dired commands, such as sorting (use the
 sort utility through call-process-region) and
 setting file modes (use set-file-modes).

* Make display.c record inverse-video-ness on
 a character by character basis.  Then make non-full-screen-width
 mode lines inverse video, and display the marked location in
 inverse video.