The codex is named after its scribe, the imperial city cantor Johann Buchmayer (c. 1520-1591). He dedicated the large-format choir book to the Regensburg City Council on 24 December 1560. It included five copies of masses and Introits, five masses composed by the composer himself, five masses arranged by Josquin Desprez (c. 1450-1521), Heinrich Isaac (c. 1450-1517) and Pierre Moulu (1480/90-c. 1550) as well as five of his own Introit motets. The adaptations that Buchmayer made to the foreign masses are motivated by practical performance considerations. He standardised difficult mensurations in the older masses to the tempus imperfectum diminutum, a duple metre, later called alla breve time. Buchmayer called this kind of metrical intervention "resoluta". As far as is known, such editing was used exclusively by him and accentuates the historical significance of the Regensburg source. The effort to fill long pauses in the older masses with new voices in favour of a fuller sound is also interesting in terms of the history of its reception.