AJAX loading of data-heavy content. When a data-heavy Ensembl page such as 'Region in Detail" is requested, the server immediately returns the page template with its navigation links, plus cached images such as small-scale overviews. The main image, however, is generated in the background, and a placeholder graphic (the e! logo within an animated spinner) is shown instead. After a few seconds the placeholder will disappear and the full image is loaded onto the page.