A certain amount of metadata is already provided for Web site resources using the Hypertext Markup Language (HTML). For example, when we wrote this page, we added HTML statements containing key words that describe the content of this definition and that are used by search engines for indexing. We also added a one-sentence description that can be shown by search engines. (These statements, called META tag statements, are invisible to you unless you click on this page and then right-click on "View source"). Less formally, the "Created on" or "Updated on" date at the bottom of this definition is also metadata - that is, data that tells you something about the data or content on this page. These are simply a few examples of many possible existing and future resource descriptions needed about a Web resource