text: By far the most numerous, mobile and expansionist migrations were those of Ijekavian-Shtokavian speakers of eastern Herzegovina, who have spread into most of Western Serbia, many areas of eastern and western Bosnia, large swathes of Croatia (Banovina, Kordun, Lika, parts of Gorski kotar, continental parts of northern Dalmatia, some places north of Kupa, parts of Slavonia, southeastern Baranya etc.). This is the reason Eastern Herzegovinian is the most spoken Serbo-Croatian dialect today, and why its name is only descriptive of its area of origin. These migrations also played a pivotal role in the spread of Neo-Shtokavian innovations.
  Earliest texts of Shtokavian dialect
  Proto-Shtokavian, or Church Slavic with elements of nascent Shtokavian, were recorded in legal documents like the charter of Ban Kulin, regulating the commerce between Bosnia and Dubrovnik in Croatia, dated 1189, and in liturgical texts like Gršković's and Mihanović's fragments, , in southern Bosnia or Herzegovina. Experts' opinions are divided with regard to the extent these texts, especially the Kulin ban parchment, contain contemporary Shtokavian vernacular. Numerous legal and commercial documents from pre-Ottoman Bosnia, Hum, Serbia, Zeta, and southern Dalmatia, especially Dubrovnik are mainly Shtokavian, with elements of Church Slavic. The first major comprehensive vernacular Shtokavian text is the Vatican Croatian Prayer Book, written in Dubrovnik a decade or two before 1400. In the next two centuries Shtokavian vernacular texts had been written mainly in Dubrovnik, other Adriatic cities and islands influenced by Dubrovnik, as well as in Bosnia, by Bosnian Franciscans and Bosnian Muslim vernacular aljamiado literature – the first example being "Chirvat-türkisi" or "Croatian song", dated 1589.