Messa di voce hairpins are single gradual dynamic items that appear as a pair of hairpins without an immediate dynamic in the middle. They indicate that within their duration, the volume either increases then decreases, or decreases then increases.
In Write mode, messa di voce hairpins have three handles: one at the start, one at the end, and one in the center. This is different to separate, ungrouped hairpins, which each have a handle at the start and end.
In Engrave mode, messa di voce hairpins have center handles that control their center aperture only. You cannot move the graphical peak of messa di voce hairpins, except by adjusting the note spacing.