Greenstone 3 feature.
Only partially developed.
To enable this, (from 22 Feb 2022):
<init-param>
<param-name>documentbasket</param-name>
<param-value>true</param-value>
</init-param>
Login as admin (or someone with editing rights?), make sure editing mode is enabled (by navigating to a document and clicking the dropdown menu until the admin button at the top)
set documentbasket=on as a cgi param.