' is used,
commands give only essential feedback (e.g., errors).

Once the new mode is created, use '/set format', '/set prompt' and '/set truncation'
to configure it.  Use '/set feedback' to use the new mode.

When the '-retain' option is used (without the '-delete' option), the mode (including
its current prompt, format, and truncation settings) will be stored for use in
future runs of the jshell tool.  If retain is not used, the mode is only defined in
the current session. After updating the mode's settings, retain the mode again to
preserve the updates across sessions.

When only the '-delete' option is used, the mode is deleted from the current session.
When both '-retain' and '-delete' are used, the mode is deleted from the current and
future sessions.

When the form without options is used, the mode settings are displayed.
When the <mode> is specified, only the mode settings for that mode are shown.
Note: the settings for the mode include the settings for prompt, format, and
truncation.
Example:
	/set mode mymode

shows the mode, prompt, format, and truncation settings for the mode mymode