Rebasing 2 Branches Simultaneously

On top of n we have 3 branches (I'll name them by their tip Change ID):

• rt, which introduces CSS.
• zx, where new functionalities are.
• o, which contains the manual.

  ○  rt       Minimal CSS css                     <- this
  │ ○  zx       Click alternates Xs and Os main   <- this
  │ ○  v        Click sets an X
  │ ○  s        Square has state
  ├─╯
  │ ○  o        Play instructions manual          <- this
  │ ○  kx       Play manual
  ├─╯
  ○  n        Square is interactive
  ~

We decide to include CSS in the other 2 branches. So, your goal is to rebase both zx and o on top of rt.
You could do this with:

    jj rebase -r kx:: -o rt

followed by

    jj rebase -r s:: -o rt

Would you be able to do this in 1 command?

jj rebase -r 'kx:: | s::' -o rt
  
○  zx       Click alternates Xs and Os main*
○  v        Click sets an X
○  s        Square has state
│ ○  o        Play instructions manual*
│ ○  kx       Play manual
├─╯
○  rt       Minimal CSS css
│ ~
├─╯
○  n        Square is interactive

Rebasing multiple branches is especially handy for keeping them up to date with trunk. Check out rebase-all, an alias by Steve Klabnik, you'll love it: you just run jj rebase-all so your local work is always based on the latest main.
People invented all sorts of amazing aliases: find them at https://github.com/jj-vcs/jj/discussions/8484.

Preview of Revsets

You should never fear a rebase: after all, you can always resort to jj undo. Also, you can always obtain a preview of the Changes involved in a Revset expression using log:

   jj log -r 'kx:: | s::'
   ○  zx       Click alternates Xs and Os main*
   ○  v        Click sets an X
   ○  s        Square has state
   │
   ~

   ○  o        Play instructions manual*
   ○  kx       Play manual
   │
   ~

Universality of Revsets

Oh, and by the way: once you have defined a Revset expression, you can use it with many commands:

• Want to delete all those Changes? jj abandon -r 'kx:: | s::'
• Want to inspect all of them? jj show -r 'kx:: | s::'
• Want to change their author? jj metaedit -r 'kx:: | s::' --update-author "Joe Doe"

That's a general trait: Jujutsu has few building blocks, but they combine in countless ways.