Reliably trapping end of paragraph / return to vertical mode

David Carlisle d.p.carlisle at
Wed Oct 2 22:17:52 CEST 2019

On Wed, 2 Oct 2019 at 21:14, William F Hammond via texhax <texhax at>

> "Taylor, P" <P.Taylor at> writes in part:
> > ...  Although Knuth provides \everypar, which can be
> > reliably used to trap entry to a paragraph, there does not
> > appear (to me, at least) to be any 100% reliable method of
> > trapping exit therefrom, and of course once the next
> > paragraph has been entered, the previous (and desired)
> > value of \prevgraf has been lost.  ...
> I'm going to present what is going through my mind as a list
> of questions.  I am not in urgent need of answers for
> myself.
> 1.  Does \par begin or end a paragraph?
end (the \par primitive), the \par token can do anything it is defined to do

> 2.  Does a blank line begin or end a paragraph?
with normal catcode and endlinechar settings  it generates a \par token
then does whatever \par is defined to be

> 3.  Is there any difference at all between \par
>     and a blank line?

not with normal settings (verbatim etc changes this)

> 4.  For the previous questions is there any difference
>     between plainTeX and LaTeX?
not really except that latex redefines the \par token not to be the \par
primitive in a lot more places than plain does,

>                               -- Bill
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