The Package Document collection element [Publications301] is used to identify the presence of Distributable Objects embedded within an EPUB Rendition, enumerate its resources and indicate its reading order. (idpf.org)
An embedded Preview is defined in a Package Document collection element [Publications301] with the role attribute value «preview». (idpf.org)
These are identified by using a child collection element with role = «index - group»: (idpf.org)