[SimonSapin]

Patrick refers to parallel layout here: in a text with many paragraphs for example, the contents of each paragraph can be laid out in parallel with other paragraphs. Then you only need to sum up the heights of earlier paragraphs to find the vertical position of each.

When printing though, you don’t know where to start page 10 until you’ve done the layout of earlier pages. There may still be some parallelism opportunity, but less than on screen.