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
{
		return getStringProperty( GroupElement.ON_PREPARE_METHOD );
	}
	/**
	 * Sets the on-prepare script of the group element.
	 * 
	 * @param script
	 *            the script to set
	 * @throws SemanticException
	 *             if the method is locked.
	 * 
	 * @see #getOnPrepare()
	 */
	public void setOnPrepare( String script ) throws SemanticException
	{
		setProperty( GroupElement.ON_PREPARE_METHOD, script );
	}
	/**
	 * Tests whether to repeat the headings at the top of each page.
	 * 
	 * @return <code>true</code> if repeat the headings, otherwise
	 *         <code>false</code>.
	 */
	public boolean repeatHeader( )
	{
		return getBooleanProperty( REPEAT_HEADER_PROP );
	}
	/**
	 * Sets whether to repeat the headings at the top of each page.
	 *