Embodiments of the invention are concerned with displaying a data set within a display area of a display device, where the data set includes a plurality of groups of elements, each of the groups including a higher-level element and one or more lower-level elements. Each element may for example form part of a Document Object Model for an HTML document.Elements are processed to identify and render one or more elements in the display area. An element is identified if the region it occupies corresponds with a selected portion of a layout area of the data set. Groups of elements are processed differently in dependence on whether a higher-level element of a group has a pre-defined spatial relationship with respect to one or more lower-level elements in the group, allowing the invention to efficiently process elements which are members of groups for which the pre-defined spatial relationship has been identified.