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
*            the maximum number of operations that should be kept in the
	 *            undo or redo history for the specified context. Must not be
	 *            negative.
	 */
	void setLimit(IUndoContext context, int limit);
	/**
	 * <p>
	 * Undo the most recently executed operation in the given context
	 * </p>
	 * 
	 * @param context
	 *            the context to be undone
	 * @param monitor
	 *            the progress monitor to be used for the undo, 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.
	 * 
	 * @return the IStatus indicating whether the undo succeeded.
	 * 
	 * <p>
	 * The severity code in the returned status describes whether the operation
	 * succeeded and whether it remains in the history. <code>OK</code>
	 * severity indicates that the undo operation was successful. The operation
	 * will be placed on the redo history, provided it can be redone (answers
	 * <code>true</code> to {@link IUndoableOperation#canRedo()}). Listeners