Last night, I wrote:
> What is the cleanest way to do this with Expl3? Specifically, what are
> the Expl3 equivalents of `\parbox` and `\llap`, at least in the way
> this code uses them?
> (I understand that `\raggedleft` would be in a very different layer of
> the code [the galley?] and probably doesn’t have a useable Expl3
> equivalent yet; and that using `\tex_kern:D` is no clearer than
> `\kern`, and that its Expl3ization will probably be in the fonts
> module. On the other hand, I see that l3trial/xfont/xfss.dtx includes
> a definition for `\mode_leave_vertical:` so perhaps I’ll copy its
> definition and use that.)

Hunting around the latex3 repository it seems I’m anticipating what
l3trial/xbox is doing. (It’s not stable, I understand, but is xbox in
a somewhat usable state if I take it from the repository? I’m quite
willing to change my [private] code as xbox updates, assuming the
current state at least broadly approximates future plans.)

Experimentation, and looking at xbox code, shows me that
`\hbox_overlap_left:n` can substitute for `\llap`. I’m not sure why
l3trial/xbox’s `\llap` includes `\xbox_leave_vmode:`, though—probably
for the same reason the Memoir example code included `\leavevmode`,
but I don’t understand that either; it seems to work just fine without

The commit message at
<> indicates that xbox
does not yet have the equivalent of `\parbox`. For the restricted use
I’m putting this to (`\parbox[t][0pt]{\somedim}{one or two lines of
text}`), can somebody suggest a lightweight alternative? Neither
wrapping `\hbox_to_wd:nn` within `\vbox_to_zero:n` nor the other way
around worked for me.

—Joel C. Salomon