built-in default editor will be used.

If the -delete option is specified, previous settings are ignored -- the editor
settings are initialized as when starting the jshell tool.  Specifically, if there
is a retained setting it is used (unless both -retain and -delete are specified --
which deletes the retained setting), if one of these environment variables is set
it will be used: JSHELLEDITOR, VISUAL, or EDITOR (in that order).  Otherwise the
built-in default editor will be used.

If <command> is specified, it will be used as the external editor. The <command>
consists of the program and zero or more program arguments.  When <command>
is used, the temporary file to edit will be appended as the last argument.
Normally, edit mode will last until the external editor exits. Some external editors
will exit immediately (for example, if the edit window exists) either external editor
flags should be used to prevent immediate exit, or the -wait option should be used to
prompt the user to indicate when edit mode should end.

Note: while in edit mode no command inputs are seen.  After leaving edit mode changes
to the edited snippets are not seen.

When the -retain option is used, the setting will be used in this and future
runs of the jshell tool.

The form without <command> or options shows the editor setting.