In addition to the above list of characteristics that set Kajkavian apart from Shtokavian, research suggests possible a closer relation with Kajkavian and the Slovak language, especially with the Central Slovak dialects upon which standard Slovak is based. As modern-day Hungary used to be populated by Slavic-speaking peoples prior to the arrival of Hungarians, there have been hypotheses on possible common innovations of future West and South Slavic speakers of that area. Kajkavian is the most prominent of the South Slavic speeches in sharing the most features that could potentially be common Pannonian innovations.