Bug 138562 Splite extendsexcpetion to seperate sub class
The suggestion is Parent invalid Cycle extends Different type extends Not top level extends
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/core/DesignElement.java
import org.eclipse.birt.report.model.api.command.ContentException;
import org.eclipse.birt.report.model.api.command.ExtendsException;
import org.eclipse.birt.report.model.api.command.PropertyNameException;
import org.eclipse.birt.report.model.api.core.IDesignElement;
import org.eclipse.birt.report.model.api.core.IStructure;
import org.eclipse.birt.report.model.api.core.Listener;
import org.eclipse.birt.report.model.api.core.UserPropertyDefn;
import org.eclipse.birt.report.model.api.elements.ReportDesignConstants;
import org.eclipse.birt.report.model.api.elements.structures.PropertyMask;
import org.eclipse.birt.report.model.api.metadata.IElementDefn;
import org.eclipse.birt.report.model.api.metadata.IObjectDefn;
import org.eclipse.birt.report.model.api.metadata.ISlotDefn;
import org.eclipse.birt.report.model.api.metadata.PropertyValueException;
import org.eclipse.birt.report.model.api.util.StringUtil;
import org.eclipse.birt.report.model.api.validators.SimpleListValidator;
import org.eclipse.birt.report.model.api.validators.StructureListValidator;
import org.eclipse.birt.report.model.api.validators.UnsupportedElementValidator;
import org.eclipse.birt.report.model.elements.ElementVisitor;
import org.eclipse.birt.report.model.elements.Library;
import org.eclipse.birt.report.model.elements.ListingElement;
import org.eclipse.birt.report.model.elements.MasterPage;
import org.eclipse.birt.report.model.elements.ReportDesign;
import org.eclipse.birt.report.model.elements.TemplateElement;
import org.eclipse.birt.report.model.elements.TemplateParameterDefinition;
import org.eclipse.birt.report.model.elements.Theme;
import org.eclipse.birt.report.model.elements.interfaces.IDesignElementModel;
import org.eclipse.birt.report.model.metadata.BooleanPropertyType;
import org.eclipse.birt.report.model.metadata.ElementDefn;
import org.eclipse.birt.report.model.metadata.ElementPropertyDefn;
import org.eclipse.birt.report.model.metadata.ElementRefPropertyType;