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
import org.eclipse.birt.report.model.api.metadata.IChoiceSet;
import org.eclipse.birt.report.model.api.metadata.IPropertyType;
import org.eclipse.birt.report.model.api.metadata.PropertyValueException;
import org.eclipse.birt.report.model.api.util.DimensionUtil;
import org.eclipse.birt.report.model.api.util.StringUtil;
import org.eclipse.birt.report.model.core.Module;
/**
 * Dimension property type. Dimension property values have two parts:
 * <p>
 * <dl>
 * <dt><strong>Measure </strong></dt>
 * <dd>A numeric measurement expressed as a Java double.</dd>
 * 
 * <dt><strong>Optional units </strong></dt>
 * <dd>The units of the dimension expressed using one of the unit specifiers
 * defined in
 * {@link org.eclipse.birt.report.model.api.elements.DesignChoiceConstants }:
 * <ul>
 * <li>in (inches)</li>
 * <li>mm (millimeters)</li>
 * <li>cm (centimeters)</li>
 * <li>pt (points)</li>
 * <li>pc (Picas)</li>
 * <li>px (pixels)</li>
 * <li>em (the height of the element's font )</li>
 * <li>ex (x-height)</li>
 * <li>% (percentage)
 * <li>
 * </ul>
 * </dd>