The container file (container.xml) primarily contains a reference to the package (.opf) document.
<?xml version="1.0"?><container version=“1.0" xmlns="urn:oasis:names:tc:opendocument:xmlns:container"> <rootfiles> <rootfile full-path="OEBPS/content.opf" media-type="application/oebps-package+xml"/> </rootfiles></container>