I am editing a longtable. Some of my cells contain a lot of text. Page breaks seem to happen only where table rows end/begin. I'd like, however, for the rows to span pages; it's fine with me if, for example, the first few lines of a row are at the end of one page and the rest of the row's lines are on the next page.
It is not in general possible. Consider if one cell is a large image and the next cell is text how would it break?
p columns are essentially
\parboxes that do not break.
pagebreaks inside a cell are in general not possible but you can work with a trick if you really need a break. However, it makes no sense if you have a lot of such tables or pagebreaks.
Set the long table as usual and have a look into the pdf output of the cell where a pagebreak maybe usefull. Now insert in that cell at the last word of that line
first col & ... some text\parfillskip=0pt \tabularnewline & and the follwing text which is on the next page.
\parfillskip=0pt you'll get a left and right justified line.