visvowref <- bibentry(bibtype   = "InCollection",
                      year      = "2018",
                      author    = "Wilbert Heeringa and Hans Van de Velde",
                      title     = "Visible Vowels: a Tool for the Visualization of Vowel Variation",
                      booktitle = "Proceedings CLARIN Annual Conference 2018, 8 - 10 October, Pisa, Italy",
                      publisher = "CLARIN ERIC",
                      pages     = "120 - 123",
                      url       = "https://office.clarin.eu/v/CE-2018-1292-CLARIN2018_ConferenceProceedings.pdf")