Bug 214212 Problem occurs when set the masterpage margin with ems/exs/pixcel units.
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/metadata/DimensionPropertyType.java
* it into a <code>DimensionValue</code>. The validation will use
	 * {@link DimensionValue#parse(String)}to parse the xml string.
	 * 
	 * @return a <code>DimensionValue</code> that holds the measure and unit
	 *         parsed from the xml value.
	 * 
	 */
	public Object validateXml( Module module, PropertyDefn defn, String value )
			throws PropertyValueException
	{
		DimensionValue dim = DimensionValue.parse( value );
		if ( dim == null )
		{
			logger.log( Level.FINE,
					"The input string may be a blank string or without measure." 
							+ value );
			return null;
		}
		validateUnits( module, defn, dim );
		if ( !DimensionValue.DEFAULT_UNIT.equalsIgnoreCase( dim.getUnits( ) ) )
		{
			logger.log( Level.FINE,
					"return dimension value with user defined unit " 
							+ dim.toString( ) );
			return dim;
		}
		logger.log( Level.FINE, "return dimension value with default unit " 
				+ dim.getMeasure( ) );
		return new DimensionValue( dim.getMeasure( ), getDefaultUnit( module,
				defn ) );