Currently, each extension is supposed to have an 'enable' option and optionally enable_editor or enable_shell, to "to apply it only to editor/shell windows" (config-extensions.def comment).  I think the rule should be changed (see below).

Currently, the file itself does not follow its own rule.  Most editor-only options only have enable and not enable_editor.  One have enable and enable_shell=False, presumably to exclude the shell, but a user could override False with True, in the user config-extensions, which would not be valid.  The file should be changed to follow the current or altered rule.

I think that the requirement should be for the presence of any one of the enable options.  An extension that is only valid for the editor should simply have enable_editor.  Ditto for enable_shell. Enable by itself would globally turn the extension on or all for all windows, include output windows.  It is possible that we might need an enable_output option too.