Bug 118429 [DataBinding] Validation should use IStatus, not just Strings
In order to use data binding in Workbench or IDE dialogs and preference pages, we need validation in terms of IStatus objects. Using strings is too simplistic. For example, look at the wizard for creating a new class. You will get a warning if the class name does not start with an uppercase letter, or if you don't provide a package name, but you will still be able to click "Finish" to proceed anyway. (Note that IStatus is currently not on the classpath, we need to re-introduce the dependency on org.eclipse.equinox.common, which contains IStatus etc.)
bundles/org.eclipse.core.databinding/src/org/eclipse/core/databinding/BindingEvent.java
public int pipelinePosition;
	
	/**
	 * The current ValidationError object (if there is one).
	 */
	public ValidationError validationError;
	/**
	 * Holds the value that was retrieved from the source updatable. Setting the
	 * value of this field changes the value that will be processed by all
	 * subsequent steps in the data flow pipeline.
	 */
	public Object originalValue = null;
	/**
	 * Holds the value that will be copied into the final updatable. This value
	 * is null if the original value has not been converted into the final
	 * updatable's data type or if no conversion will be performed. Setting the
	 * value of this field changes the value that will be processed by all
	 * subsequent steps in the data flow pipeline.
	 */
	public Object convertedValue = null;
	/**
	 * A constant indicating that this event is occuring during a copy from
	 * model to target.
	 */
	public static final int EVENT_COPY_TO_TARGET = 0;
	/**
	 * A constant indicating that this event is occuring during a copy from
	 * target to model.
	 */
	public static final int EVENT_COPY_TO_MODEL = 1;