 From a linguistic point of view, they illustrate the changes in the Bulgarian language in the 13th–14th century, such as the gradual disintegration of the case system, and the number and type of loanwords.Being some of the few secular sources on the Bulgarian history in the Middle Ages, the charters are of great interest to the researchers of medieval Bulgarian law, as they list contemporary terms for different forms of taxes, agreements, penalties, etc.Most of the charters also enumerate personal names and toponyms, hinting at the development of the name system among the Bulgarians and confirming the medieval existence of many villages and towns, mostly in modern Bulgaria (largely in and near Rila) and North Macedonia (predominantly around Skopje).