2.1.1559 Part 1 Section, userInterface (User Interface)

a.   The standard states that when this element is true, protection applies to the user interface only.

Office always applies protection to the user interface when this element is present, regardless of the value the val attribute.

b.   The standard states that this element specifies that the protection applies to the user interface only, and not to changes made through the object model.

Office does not provide a way to set this property or save a file with this element.  On load this element is treated as specifying standard protection.