The <fo:footnote> object defines a footnote within the region-body of a page.
It is an error if an <fo:footnote> occurs as a descendant of a flow that is not assigned to a region-body.
It is also an error if an <fo:footnote> occurs as a descendant of an fo:block-container that generates absolutely positioned areas.
Additionally the <fo:footnote> object cannot have an <fo:float>, <fo:footnote>, or <fo:marker> as a descendant.
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