[pdftex] 1px is not 1bp which seems to contradict the pdftex manual

[Karl Berry]

I asked Hans, who (partly) originated the px dimension in pdftex, back
in 2005 (pdfTeX 3.141592-1.21a), according to the pdftexdir/NEWS file.

Not related to CSS. (I think it predates the (re)definition of px=1/96in 
in CSS, or at least was independent. In fact, I speculate that the css
redefinition is why \pdfpxdimen got created a few years later.)

I welcome counterexamples, but I see no practical use for it. And there
don't seem to be any real-world documents in the TeX universe using it.  -k


Date: Mon, 27 Mar 2023 23:16:38 +0200
From: Hans Hagen

I think that it was introduced in order to deal with bitmap inclusion of
png files that lacked resolution information and then defining in pixels
(html inherited mess). So one could define sizes in pixels and
afterwards change the scaling with normal and downsampled variants.

But I cannot find any document on my disk that actually uses it. [...]