Among the manuscripts in the collection of the University Library in Wrocław there is a codex created in the first decades of the 15th century that contains nearly 150 various texts in Latin, German, Czech and certainly Polish. They were written down by a Franciscan friar, Mikołaj of Koźle. His life in the clergy perfectly demonstrates the winding paths of the medieval Silesians and provides a partial explanation of the phenomenon of their multilingualism. He joined the Order in Głogówek (in the Czech-Polish Franciscan province), where he completed his basic education. Then he took his religious vows in 1415 at the monastery in the Czech city of Czesławiec; he later stayed at monasteries in Olomouc and Krnov to return from the Hussite Czech Republic to Silesia in 1431 and reside in the monastery in his home city of Koźle.

The entire literary output of Mikołaj is contained in the codex. It includes sermons, chronicle entries, poems, prayers, religious songs and secular works. Cantilena inhonesta (Indecent Ditty) is widely known. It is considered the oldest Polish love song. In this frivolous work – now barely legible, as it was carefully covered over with ink in the codex – Polish and Czech linguistic forms are mixed.