This already is implemented.
- Place caret where you want to start the hairpin.
- Type < or > (no need for the popover, but the popover works too)
- Use the right arrow key to advance the caret to where you want the hairpin to end.
- Type ? (yes, a question mark)
The hairpin will not appear at all until you’ve completed all four steps.
Alternatively,
- Place caret where you want to start the hairpin.
- Type < or > (no need for the popover, but the popover works too)
- Type the duration you’d like the hairpin to be, e.g. if you’d like a hairpin that lasts for a quarter/crotchet, type 6.
- Hit Space. (Optionally continue hitting Space to extend the hairpin by the selected duration.)
Again, the hairpin won’t appear at all until you’ve completed all four steps.