Following up on this matter (I let it go when the Dorico 3 release fever was running high).
I did some research (I’m using a Sostenuto mood marking in my thesis composition and referencing it in my dissertation; I didn’t want to be committing an error). For the most part, it does just mean sustained, no tempo change, but there are also references where it sometimes can mean a slackening of tempo. So we’re both right!
It would be great to have the option to have Sostenuto as a mood marking or a gradual tempo change in future versions of Dorico? This is obviously not top priority; as I mentioned above, there is a hack to getting a tempo/mood marking for Sostenuto and avoid the gradual tempo quality.
Mood marking references:
“a movement or passage whose notes are markedly prolonged. sustained to or beyond the note’s full value —used as a direction in music” Sostenuto Definition & Meaning - Merriam-Webster
Screenshots of:
Gerhkens 1921 _ Music Notation and Terminology
Baker 1907 - Dictionary of Musical Terms
Riemann 1896 - Dictionary of Music
Sustained, with sometimes a tempo change references:
“sostenuto — sustained, sometimes with a slackening of tempo” http://www.goodwinshighend.com/music/classical/tempo_glossary.htm
“A direction that has been used both to designate a style of playing and as a tempo mark or modification; the abbreviation sost. is common. It is occasionally used to indicate a slowing down (e.g. in Brahms and Puccini; Brahms wavered, for the slow movement of his first symphony, between poco adagio and andante sostenuto). The words ‘sostenende’ and ‘sostenente’ (present participle) are also found and are perhaps more precise. The ‘sostenuto’ pedal on a piano is the one that sustains notes by lifting the dampers from the strings.” Fallows, D. (2001). Sostenuto. Grove Music Online.
"Sustained, sustaining in duration; sometimes with the implication of a slowing in tempo."Sostenuto, Sostenendo -LSB-It.,Abbr.Sost.-RSB-. (2003). In D. M. Randel (Ed.), The harvard dictionary of music (4th ed.). Cambridge, MA: Harvard University Press.
