Reflowable documents cannot be designated in spreads #1652
Description
If a spine item references a reflowable epub content document (rendition:layout=reflowable with no local spine override, or rendition:layout-pre-paginated with a local rendition:layout-reflowable override), it must not have any of the spread placement properties listed in its properties attribute.
Those properties are: page-spread-right, rendition:page-spread-right, page-spread-left, rendition:page-spread-left, and rendition:page-spread-center