Semantically, header navigation lists should always be marked up as html lists, even if what appears on the page looks more like a collection of folder tab graphics. This semantic handling of header lists has powerful advantages for universal accessibility and helps clarify your site organization for search engines. Designers can use Cascading Style Sheets to style lists of navigation links to look like tabs. Opera’s page headers are minimalist tabs but convey every essential page header function in a compact design (fig. 4.18, bottom).