A device user interface in which computer functionality is invoked by user interaction with dynamically generated interface regions of a writing surface. A computer system identifies a marking written on the writing surface or a user selection of an existing written marking. Adjacent to the marking, the computer system automatically generates one or more interface regions associated with the marking. User interaction with one of these regions automatically invokes computer functionality related to the interacted region. A different function may be invoked by each region. The computer system dynamically positions and may dynamically size the interface regions based on the position (and size) of the marking. Multiple markings yield multiple regions, with different regions associated with respective markings. In one embodiment, the regions are established in front of and/or after a written word. Regions may also be established on top of and/or below the written word, for example. In another embodiment, the computer system is a pen-based interactive computer system.