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/api/validators/ElementExtendsValidator.java
/*******************************************************************************
 * Copyright (c) 2004 Actuate Corporation.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *  Actuate Corporation  - initial API and implementation
 *******************************************************************************/
package org.eclipse.birt.report.model.api.validators;
import java.util.ArrayList;
import java.util.List;
import org.eclipse.birt.report.model.api.command.ExtendsException;
import org.eclipse.birt.report.model.api.util.StringUtil;
import org.eclipse.birt.report.model.core.DesignElement;
import org.eclipse.birt.report.model.core.Module;
import org.eclipse.birt.report.model.validators.AbstractElementValidator;
/**
 * Validates the element extends property. If the value can refer to an actual
 * element, it will be resolved after validation.
 * <h3>Rule</h3>
 * The rule is that the element extends value should refer to an actual element
 * in the same report or included libraries.
 * <h3>Applicability</h3>
 * This validator is only applied to the element extends property.
 */
public class ElementExtendsValidator extends AbstractElementValidator