How to prevent strechtability?

[Rodolfo Medina]

Heiko Oberdiek via texhax <texhax at tug.org> writes:

> On 2019-06-21 13:34, Rodolfo Medina wrote:
>>
>> in the following example, to process with simply `tex test', I'd like that
>> `hallo' was not so far from the hrule above.  How can I prevent
>> stretchability in that place?
>
>>    \hrule\vskip.1in
>> hallo
>>    \vskip .1in\hrule\vskip 1cm
>
> The stretchability is inserted by \parskip (0pt plus 1pt), when "hallo"
> starts a new paragraph. This can be prevented by locally removing the
> stretchable component of \parskip when starting the paragraph for "hallo":
>
> \hrule
> \vskip.1in
> \begingroup\parskip=0pt \leavevmode\endgroup
> hallo
> \vskip .1in
> \hrule
> \vskip 1cm


Thanks, David and Heiko...

\raggebottom is not what I want, \parskip=0pt is ok.  But, out of curiosity:
why does TeX choose to stretch only there, between `\hrule' and `hallo', and
not between `hallo' and the following `\hrule'?  There should be a \parskip
there as well...

Cheers,

Rodolfo