Users can construct indexes by creating lists of URLs. Most client programs allow people to do this easily. Many users then advertise these hotlists by adding them to their own pages in their own web servers. Some sites keep hotlists or bookmarks organised by subject or by research interest. Some sites even let users submit new entries for their indexes. This allows navigation (although it doesn't really help searching) in the Web. Each hotlist or list of bookmarks represents another tour or view of the places of interest to the author of that hotlist. As more and more sites and users construct such lists, the density or value of referenced information increases.