Oh yes, `\ \ \ \ ` would be pretty good. (My brain thought they'd be

concatenated for some reason and I didn't try it. Distracted by other work,

I suppose.)

They're actually lost nowhere (e.g., not even after unfinished f-expansion)

I'm probably happy to leave things as they are for now. In fact, any sort of

"indent" function would be better if it respected the line-wrapping routine

and that's more work than it's worth right now. I'll table this thought in

the Github wiki.

Do you mean \msg_indent:n {<text to indent that may be line-wrapped>} ?