Methods to support the creation of multi-device user interfaces typically use some type of abstraction of the user interface design. To retrieve the final user interface from the abstraction a transformation will be applied that specializes the abstraction for a particular target platform. The User Interface Markup Language (UIML) offers a way to create multi-device user interface descriptions while maintaining the consistency of certain aspects of a user interface across platforms. We extended the UIML language with support for layout constraints. Designers can create layout templates based on constraints that limit the ways a user interface can rearrange across platforms. This results in a higher degree of consistency and reusability of interface designs.