Bug 123972 [Undo] Support approval of undoable operation execution
In GMF we do some common validation on our commands before we proceed to execute, undo or redo them. This validation is external to the command's ability to execute, undo or redo itself. Registering an IOperationApprover with the operation history for this of validation would give us an elegant solution. However, the IOperationApprover only supports approval of undo and redo. We also require support for approval of operation execution. Would you consider adding a proceedExecuting() method to the IOperationApprover interface, or to an extension of the IOperationApprover interface?
bundles/org.eclipse.core.commands/src/org/eclipse/core/commands/operations/IOperationHistory.java
*/
	void operationChanged(IUndoableOperation operation);
	/**
	 * <p>
	 * Get the operation that will next be undone in the given undo context.
	 * </p>
	 * 
	 * @param context
	 *            the context for the undo
	 * @return the operation to be undone or <code>null</code> if there is no
	 *         operation available. There is no guarantee that the available
	 *         operation is valid for the undo.
	 */
	IUndoableOperation getUndoOperation(IUndoContext context);
	/**
	 * <p>
	 * Redo the most recently undone operation in the given context
	 * </p>
	 * 
	 * @param context
	 *            the context to be redone
	 * @param monitor
	 *            the progress monitor to be used for the redo, or
	 *            <code>null</code> if no progress monitor is provided.
	 * @param info
	 *            the IAdaptable (or <code>null</code>) provided by the
	 *            caller in order to supply UI information for prompting the
	 *            user if necessary. When this parameter is not
	 *            <code>null</code>, it should minimally contain an adapter
	 *            for the org.eclipse.swt.widgets.Shell.class.