Issue #22065: Try the delete demohelp.txt part again.

Lib/turtledemo/demohelp.txt

-
-
-  ----------------------------------------------
-
-      turtleDemo - Help
-
-  ----------------------------------------------
-
-  This document has two sections:
-
-  (1) How to use the demo viewer
-  (2) How to add your own demos to the demo repository
-
-
-  (1) How to use the demo viewer.
-
-  Select a demoscript from the example menu.
-  The (syntax coloured) source code appears in the left
-  source code window. IT CANNOT BE EDITED, but ONLY VIEWED!
-
-  - Press START button to start the demo.
-  - Stop execution by pressing the STOP button.
-  - Clear screen by pressing the CLEAR button.
-  - Restart by pressing the START button again.
-
-  SPECIAL demos are those which run EVENTDRIVEN.
-  (For example clock.py - or oldTurtleDemo.py which
-  in the end expects a mouse click.):
-
-      Press START button to start the demo.
-
-      - Until the EVENTLOOP is entered everything works
-      as in an ordinary demo script.
-
-      - When the EVENTLOOP is entered, you control the
-      application by using the mouse and/or keys (or it's
-      controlled by some timer events)
-      To stop it you can and must press the STOP button.
-
-      While the EVENTLOOP is running, the examples menu is disabled.
-
-      - Only after having pressed the STOP button, you may
-      restart it or choose another example script.
-
-   * * * * * * * *
-   In some rare situations there may occur interferences/conflicts
-   between events concerning the demo script and those concerning the
-   demo-viewer. (They run in the same process.) Strange behaviour may be
-   the consequence and in the worst case you must close and restart the
-   viewer.
-   * * * * * * * *
-
-
-   (2) How to add your own demos to the demo repository
-
-   - Place the file in the same directory as turtledemo/__main__.py
-     IMPORTANT! When imported, the demo should not modify the system
-     by calling functions in other modules, such as sys, tkinter, or
-     turtle. Global variables should be initialized in main().
-
-   - The code must contain a main() function which will
-     be executed by the viewer (see provided example scripts).
-     It may return a string which will be displayed in the Label below
-     the source code window (when execution has finished.)
-
-   - In order to run mydemo.py by itself, such as during development,
-     add the following at the end of the file:
-
-    if __name__ == '__main__':
-        main()
-        mainloop()  # keep window open
-
-    python -m turtledemo.mydemo  # will then run it
-
-   - If the demo is EVENT DRIVEN, main must return the string
-     "EVENTLOOP". This informs the demo viewer that the script is
-     still running and must be stopped by the user!
-
-     If an "EVENTLOOP" demo runs by itself, as with clock, which uses
-     ontimer, or minimal_hanoi, which loops by recursion, then the
-     code should catch the turtle.Terminator exception that will be
-     raised when the user presses the STOP button.  (Paint is not such
-     a demo; it only acts in response to mouse clicks and movements.)