One sometimes needs to specify the point / time at which one takes the derivative, using a vertical bar.

In typst, this can be approximated using

dv(,t)| _(t=0) f(t)

which kind of works but looks ugly since the bar is too short. It would be nice if one could use something like dv(,t, t=0) or dv(,t, at=(t=0)) which automatically yields a proper rending of the bar.

Looking at the code, typst seems to use the method stretch_vertical to increase the length of lines/bars.