Bug 151959 inappropriate screen operation
steps to reproduce: - create a report - add a grid item (3x3) - switch to Outline view - expand the grid item to see its rows and cells - select the grid item, and drag it into any of its own cell expected behavior: - is it an invalid screen operation? if it is, it should be banned actual behavior: - the grid item was disappeared surprisingly
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/core/DesignElement.java
* <li>The {@link #userProperties}member holds the user-defined property
 * definitions for this element.</li>
 * </ul>
 * <p>
 * See also the meta-data section above for the methods that validate property
 * values, and the property value section below for methods that work with
 * property values.
 * 
 * <h3>Property Values</h3>
 * 
 * See the {@link ElementPropertyDefn}class for a description of the details of
 * property values. Property values are of two key types: normal and intrinsic.
 * Normal properties are stored in the {@link #propValues}member on this class.
 * Intrinsic properties are stored in member variables.
 * <p>
 * Normal properties have two states: <em>set</em> and <em>unset</em>. A
 * property is set on element E if a value for that property appears in the
 * propValues list for element E; otherwise it is unset on element E.
 * <p>
 * Elements inherit property values from their parent elements. So, if property
 * P is unset on element E, E will inherit the value of P from its parent
 * element.
 * <p>
 * The <em>local value</em> of a property for an element E indicates whether
 * or not the property is set on that specific element. The local value is
 * generally of interest only to low-level code. The XML design file shows only
 * the local property values for an element.
 * <p>
 * The <em>effective value </em> of a property provides the value computed
 * using the property search which includes the ancestor elements, styles,