The categorisation of information is a very common practice. Categorisation can conform to domain-related taxonomies, or be suggested by the organisational culture of the environment in which the
user operates. Often, the user may need to use multiple hierarchies or require multiple characterisations to be active at the same time, or they may wish to define cross-cutting groups for special purposes. The work
developed in this paper is aimed at providing a flexible, seamless management of various ways of organising the required information. The concept of a set is adopted as the fundamental notion of information organisation, and, in particular, the familiar visual representation of sets and their relationships in terms of Euler Diagrams is used. We instrument the visualisation of sets to enable the uniform application of functions to items presented in selected diagram regions corresponding to set, or category, intersections. We present a system that realises this novel concept, together with rationale for the choices made in its development, as well as a simple scenario of use. The potential for end user development of such an interface should enhance its uptake, and we highlight various
avenues such as: macro development within the given system; user development of domain specific functionalities that extend, and can easily plug into, the given system; development of interface variations.