1. A method for restricting the customizability of a base metadata document, the base metadata document defining one or more characteristics of at least a portion of a software application, the method comprising: receiving a type-level customization policy defined for an object type of an object included in the base metadata document, the type-level customization policy indicating whether instances of objects having the object type may be customized by users of the software application; and enforcing the type-level customization policy at runtime of the software application.