Calligraphic letters

#let scr(it) = math.class("normal",
  text(font: "", stylistic-set: 1, $cal(it)$) + h(0em)
)

$ scr(A) scr(B) + scr(C), -scr(D) $
Rendered image

Unfortunately, currently just stylistic-set for math creates bad spacing. Math engine detects if the letter should be correctly spaced by whether it is the default font. However, just making it "normal" isn't enough, because than it can be reduced. That's way the snippet is as hacky as it is (probably should be located in Typstonomicon, but it's not large enough).