(Sent quickly. Please excuse brevity.)

On 19/09/2011, at 11:51 PM, Bruno Le Floch <[log in to unmask]> wrote:

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)

Yeah, silly me. 

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>} ?

Aye :-)