When a command ask to select the objects (usually with the message "select objects") you can type the letter "H" for Help to show all options.
The <WCircle> and <CCerchio> options select respectively objects that are Inside/intersecting a circle and objects only inside a circle.
The <WObjectsi> e <Cobjectsi> options select respectively objects that are Inside/intersecting existing objects and objects only inside existing objects.
The <FBuffer> e <IBuffer> options select respectively objects that are Inside/intersecting a buffer and objects only inside a buffer.