0pt confuses LaTeX's
\clearpage command and results in an extra blank page. This has been known since forever. Apparently some think that
there's no reason to set
0pt, so this is not considered a bug.
Yet there's no shortage of ugly workarounds, challenging this claim, like in the very linked page
The lesson is: Don't set
\topskip = 0pt, rather set it to, say,
0.01pt. Nobody will be the wiser but LaTeX.
Apparently people do need this setting from time to time for reasons the author of the first quote simply swiped off the table and the issue keeps popping up surprising users. I myself discovered this when I wished to reach the edges of the page with pixel accuracy. As soon as
\topskip is nonzero it will mess with such things, because even though it is fixed (even though negligible), nontrivial content-dependent calculations will take place (The TeXBook p. 114):
... TeX inserts special glue just before the first box on each page. This special glue is equal to
\topskip, except that the natural space has been decreased by the height of the first box, or it has been set to zero in lieu of a negative value.
Should zero topskip indeed be considered a taboo? If so, why? (The TeXBook gives no reason why it shouldn't be any possible dimen, except that negative does not make much sense.)
OK, my premise is wrong. Because of the old newsgroup post and another answer on this very site, I thought that this was well-known behaviour. The answers here confirm that
- it is a bug,
- it is not being tracked.
The reason indeed was curiosity, not in the least emotions like anger. I'm voting to delete this because in these circumstances it does not function as a question it was meant to be. I hope this won't cost people earned points. Sorry for the inappropriate form.