I think there is a mistake in this message :
"You can give a rating from zero to five stars to an image. The quality criteria which lead to a rating are fully up to you. Whenever you import images, each image receives a default rating which you can define in core options (see <xref linkend=\"core_options\"/>). You can later revise the rating at any time. You can also mark an image as <quote>rejected</quote> by pressing the <inlinegraphic fileref=\"images/lighttable_thumb_reject.png\" scalefit=\"1\" width=\"2%\" align=\"center\"/> icon or typing the <emphasis>r</emphasis> key. This will remove all stars. You can reverse the rejection by applying a new star rating."
We can find the default rating in GUI options and not in core options.