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
* </dl>
 * <p>
 * For example: "10mm", "12.3in", "1.5cm", "20pt" or "0.1".
 * <p>
 * The units are optional. If omitted, the units are assumed to be those
 * specified on the report design itself. Default units are always absolute. For
 * example, a U.S. developer will mostly use inches, and so the design's default
 * units would be inches. Any report dimensions in inches can omit the unit
 * suffix: the model knows they are in inches because that is the default for
 * the report.
 * <p>
 * Dimension values are stored as <code>DimensionValue</code> objects. These
 * objects store the measure as a double and the units as an string value.
 * <p>
 * The user enters dimensions as strings with the optional unit suffix. The UI
 * displays dimensions as strings, again with the optional unit suffix.
 * <p>
 * Some parts of the application will find it easier to work with specific
 * physical units. For example, the layout editor may choose to work in units in
 * millimeters. In this case, the application specifies its
 * <em>application units</em> in the design session. If the application
 * requests the dimension property as a double, this class converts the property
 * into the desired application units, taking into consideration the unit suffix
 * (if any) for the property and the design's default units (if the property
 * value has no unit suffix.)
 * 
 * @see DimensionValue
 * @see org.eclipse.birt.report.model.api.util.DimensionUtil
 */
public class DimensionPropertyType extends PropertyType