actually, i have in mind "chunking" like this:

    a chapter-header should not appear in the 
    middle, or at the bottom, of the viewport.

    initial text after a chapter-header should 
    appear in the same viewport as that header.

    the first line of a paragraph shouldn't be split
    across viewports from the rest of the paragraph.

    the last line of a paragraph should not be split
    across viewports from the rest of the paragraph.

    an image should not be split across a viewport.

    a caption for an image should appear in
    the same viewport as the image itself.

    the table-header for a table should not be
    split across viewports from the table itself.

    a table which will fit entirely within the current
    viewport should not be split across viewports.

    the caption for a table should not be split
    across viewports from the rest of the table.

    a blockquote should not be split unnecessarily
    across viewports if it'll fit on a single viewport.

    a list should not be split unnecessarily across 
    several viewports if it would fit on a single one.

    a description term should appear on a viewport with
    its description definitions, to the extent possible.
 
    the last paragraph of a chapter shouldn't appear on
    a separate viewport from the rest of the chapter.

    any two contiguous chunks of text which refer to
    each other should be shown on the same viewport.

    the cover-page for a document shouldn't be split
    across multiple viewports, if at all possible.

    a dedication page shouldn't be split across viewports.