Bug 161174 Expect to set/get interval range with a 'String' param in GroupHandle.
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/api/GroupHandle.java
* 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;
import java.util.Collections;
import java.util.Iterator;
import org.eclipse.birt.report.model.api.activity.SemanticException;
import org.eclipse.birt.report.model.api.command.NameException;
import org.eclipse.birt.report.model.api.elements.structures.ComputedColumn;
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.elements.GroupElement;
import org.eclipse.birt.report.model.elements.Style;
import org.eclipse.birt.report.model.elements.interfaces.IGroupElementModel;
/**
 * Represents both list and table groups in the design. Groups provide a way of
 * showing common headings for a group of related rows.
 * <p>
 * A group is defined by a group key. The key is a column from the query. If the
 * group key is a time field then user often want to group on an interval such
 * as month or quarter.
 * 
 * @see org.eclipse.birt.report.model.elements.GroupElement
 * @see SlotHandle
 */
public abstract class GroupHandle extends ReportElementHandle