HTML5 is the latest version of the well-known HTML standard, a language for structuring and presenting content for the World Wide Web. Now, this new version improves the language with support for the latest multimedia while keeping it easily readable by humans and consistently understood by computers and devices. These new abilities increase the power of the language and allow the developer to create lightweight applications, where user interfaces assume a leading role that was previously inconceivable.
If you are interested in including UML diagrams as part of your application, just try this demo, which is a simple (but surprisingly complete) diagramming tool that shows some functionalities that jsUML2 provides. Notice that this editor is not conceived as a server-side application (it only contains client-side code), and no sophisticated user interface was developed, it just demonstrates the power of jsUML2. Your needs and imagination will do the rest.