The commentary indicates superficial research. The hymn Aurora lucis rutilat, eleven verses from which Light's gliittering morn and That easer day with joy was bright has it's earliest known appearance in a Frankish hymnal compiled in the 9th C., know as the Murbach hymns. Ergo, it is Ambrosian only in its 88.88 meter, not its authorship. One known copy of this document survives, and can be viewed at the Boldleian Library archives. A summary of this document can be found in their Junius Mansuscripts collection at https://archives.bodleian.ox.ac.uk/repositories/2/archival_objects/173954
The hymn itself, Latin with Old High German (Frankish) interlinear glosses, can be viewed at
verso
https://digital.bodleian.ox.ac.uk/objects/4df4cdd2-14d8-4256-ae07-a09917b3408e/surfaces/f7eab48e-a387-4e90-8d7a-51a54486e4fc/
recto
https://digital.bodleian.ox.ac.uk/objects/4df4cdd2-14d8-4256-ae07-a09917b3408e/surfaces/adc0ae3c-568a-47dd-97cb-feb828a6f698/
Comments
Very interesting!
Thanks for providing the specific links. However, it's not clear to me what "commentary" you are referring to when you say it reflects "superficial research". And the Latin original for "That Easter Day with joy was bright" is given as "Claro Paschali gaudio", not "Aurora lucis rutilat" (though the former may well be embedded in the latter. The date given for "Aurora lucis rutilat" is c. 7th century, and that for "Claro Paschali gaudio" as early mediaeval, so it doesn't sound to me like anybody is stating that Ambrose personally wrote either one.