... 13.1 Introduction to paged media . ... The page area . ... Percentage values on the margin properties are relative to the dimensions of the page box ; for left and right margins, they refer to page box width while for top and bottom margins, they refer to page box height. ... A page break must occur at (1) if, among the 'page-break-after' and 'page-break-before' properties of all the elements generating boxes that meet at this margin, there is at least one with the value 'always', 'left', or 'right'...