@ Ned Deily:
Thank you for the comment's.

1. I documented it in the config-extensions.def how to make it visible on startup(or not). In the new patch, it is not visible by default.

2. I have made the changes.

4. I'll explain the reason why this argument is required:
Without this argument, if a user "selects" the sidebar Text widget, a highlight can be seen around the selected area. Adding this argument prevents it showing up.
The new patch prevents this unknown option error, by adding the inactiveselectbackground only if Tk version >= 8.5

(Because of this issue which you raised, I found a new bug and fixed it - see below.)

5. Done

6. I added a comment in the config-extensions.def file. The enable_shell option has been removed for now. It is not related to linenumbering.

@Terry Reedy:

1. Done. Disabled by default

4. I mentioned the reason why it is required above.

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New bug which was discovered because of 4 and fixed:
Scrolling on the sidebar text widget using mouse by dragging would scroll just the sidebar text widget and not the main text widget. This has been fixed by adding  self.text.yview_moveto(args[0]) in vbar_set.