Flats valid for a whole line <> reflow

[olivierberten]

No idea whether it's possible for gregorio to deal with this but I still wanted to document that case:

https://gregobase.selapa.net/chant.php?id=4214
In this chant, all first b's on each line are flattened and valid for the whole line. No idea whether it's usual practice or if it's exceptional. The problem is obviously that when the lines in the transcription don't match the original, the flats end up in an unlogical place...

[henryso]

Duplicate of #157