The treatise by Danckerts exists in three versions. The first was probably written in 1551, and Danckerts seems to have revised it twice: once around 1555 and once around 1559 or 1560. Its importance to music history is as a document by a performing musician, with strong conservative views, who documented contemporary practice in some areas – for example in interpretation of accidentals – where documentation is relatively scanty. One of the chapters in his treatise contains an account of a dispute between two singers in the papal choir over the correct application of accidentals to polyphonic parts which, as was normal at the time, contained none. Danckerts also wrote on the use of chromaticism, generally derisively, and opposed attempts to add modes to the current eight-mode system, for example as described by Glareanus in his 1547 publication, the "Dodecachordon", which proposed the twelve modes, including the major and minor scales familiar in the present day.