Were king Stefan the First-Crowned and his son Radoslav co-rulers?

The Serbian historiography considers the issue of the co-ruling of King Stefan the First-Crowned and his son Radoslav as the one finally resolved. The suggested solution on the co-rule of Stefan and Radoslav may be most succinctly expressed as following: as early as in the year of 1220, due to the frail health of Stefan the First-Crowned and Radoslav's marriage to Anne the Epirus princess, Radoslav was crowned to be the king and positioned to co-rule with his father after the Byzantine model of governing. Nevertheless this point of view has some loose ends. The notion of co-ruling and the very term of 'co-ruler' are quite freely used in the scholarly works. A general consensus on the precise meaning has not been reached yet. At the point where one author perceives a co-rule, the other categorically denies it. Basically the approach equalizing the heir to the throne and the co-ruler is wrong. Although the co-rulers in most cases were the throne heirs, they cannot be called the co-rulers because of the right to inherit the throne, but for the ruling attributes that formally established that right. The conviction of the co-rule of King Stefan and his son Radoslav is founded on the interpretation of the facts coming from the following sources: entitling charters for the monastery of i a, produced by Stefan and Radoslav around 1220; some segments from St. Sava's biographies by Domentian and Theodosius describing the circumstances of Stefan's death-bed leaving the throne to Radoslav; the three acts of the town of Kotor from 1221 and 1227 dated by the rule of king Radoslav, the portraits of Stefan and Radoslav next to the entrance to the Church of the Ascension in the monastery of i a and in the nartex of the Mile eva monastery church. In the first i a charter, Stefan calls Radoslav his heir, while in the second i a charter Stefan points out Radoslav as his first-born son blessed by him to be the king of the whole state. (jego e i blagoslovismo biti emou kralju v'se sije dr' ave). Though differently in manner, Radoslav's hereditary right has been emphasized in both of these charters. In my opinion, the formulation of the second charter does not refer to the coronation of a co-ruler, but a ceremonious act of proclaiming the successor. That may have been one of the results of Radoslav's marrying Anne the daughter of the Epirus ruler Theodore I Angelos in 1219/1220. St. Sava's biography by Domentian tells us about Stefan's appointing Radoslav for his heir immediately before his death. That was followed by arch-bishop Sava's crowning him the king to be s'presto