In UML, profiles are mechanisms to extend the UML for a specific domain or purpose. The UML specification allows for one profile to reuse or import elements from another profile. This enables modularity and encourages reusability of profile elements across different domains. Additionally, one profile may extend the stereotypes or metaclasses defined in another profile, which allows for the creation of layered profiles where each layer adds its own specificities. This is a common practice in software and systems modeling to cater to different aspects of a system within separate profiles, which are then integrated to form a comprehensive model. The capability to reuse and extend profiles is defined in the UML 2.x Superstructure Specification, which gives guidelines on how to define and use profiles within UML.