Experimental IR meets multilinguality, multimodality, and interaction 12th International Conference of the CLEF Association, CLEF 2021, virtual event, September 21-24, 2021 : proceedings - Candan, Kasim Selçuk; Ionescu, Bogdan; Goeuriot, Lorraine; Larsen, Birger; Müller, Henning; Joly, Alexis; Maistro, Maria; Piroi, Florina; Faggioli, Guglielmo; Ferro, Nicola (Information systems and applications, incl. internet/web, and HCI, 2021)