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/BindSupportFactory.java
/**
	 * Creates a converter for the given from and to types and model
	 * description. Either toType or modelDescription can be null, but not both.
	 * The returned converter (if not null) should convert values of type
	 * fromType to values of type toType (in the case that toType is given), and
	 * (in the case that modelDescription is given) convert to the type expected
	 * by updatable objects created from the given model description.
	 * 
	 * @param fromType
	 *            The type to convert from
	 * @param toType
	 *            The type to convert to, or <code>null</code> if not known
	 * @return a converter, or <code>null</code> if this factory cannot create
	 *         a converter for the given arguments.
	 */
	public IConverter createConverter(Object fromType, Object toType) {
		return null;
	}
	/**
	 * @param fromType
	 * @param toType
	 * @return whether fromType is assignable to toType, or <code>null</code>
	 *         if this factory cannot determine assignability between the given
	 *         types
	 */
	public Boolean isAssignableFromTo(Object fromType, Object toType) {
		return null;
	}
}