> I would expect the word "footer" to pop up at -2c from the page bottom, > then a page break. Footer does pop up, and there's the page break too, > however it does not show up at -2c from the bottom. It's lower.
It is working as intended. When you say ".sp |0c" in troff, that does not mean that the baseline will be at 0 cm, but rather the "top of the text" will be at 0 cm. Think of it as an approximation to lead typesetting, except that in troff the baseline will be set 1v below the specified point (i.e., one whole baseline distance, and not some fraction of the total line height as it would be in real lead typesetting). You may set the baseline separation to zero with ".vs 0", but it is best to do this in a separate environment, in order to avoid messing up the running text.
