\dontleavehmode is \dontleavehmode=\quitvmode. and \quitvmode is a primitive stricly speacking we don't see a space, but a command that switch to a mode to another. And it's also sound good: you have put a command to change status. \hskip\zeropoint\hbox{} ;-) here we see a space of 0pt. Can be a bit embarassing that "a horiz. space of 0pt" make difference between status, because one can think "hey, a space of 0pt is nothing and should do nothing!" (Of course, \hskip0t has sense ) \hskip1sp\hbox{...} here we see a space of 1sp, ie (1/2^16) * 1pt which is invisible to human eye. Here my "invisible touch" effect. It's more "human" because i can say "hey, you have inserted a hor. space very small, so small that you can see it, but it's always a hor,. space not null, so it's reasonable a change of state." btw, the context way is \dontleavehmode -- luigi ... it's new . it's powerful . it's luatex . http://www.luatex.org