Method rebase

src/ooxml/java/org/apache/poi/POIXMLDocumentPart.java:95–106

When you open something like a theme, call this to re-base the XML Document onto the core child of the current core document

(OPCPackage pkg)

     *  current core document 
     */
    protected final void rebase(OPCPackage pkg) throws InvalidFormatException {
       PackageRelationshipCollection cores =
          packagePart.getRelationshipsByType(PackageRelationshipTypes.CORE_DOCUMENT);
       if(cores.size() != 1) {
          throw new IllegalStateException(
                "Tried to rebase using " + PackageRelationshipTypes.CORE_DOCUMENT +
                " but found " + cores.size() + " parts of the right type"
          );
       }
       packageRel = cores.getRelationship(0);
       packagePart = POIXMLDocument.getTargetPart(pkg, packageRel);
    }

    /**
     * Provides access to the underlying PackagePart