Adding (and displaying) markers is by far the most common need, but it is specialization of a more general capability, which is to allow the user to input (any) simple features geometry. Multiple markers might be a "multipoint" type geometry, or it might be multiple points. This capability also leads into a discussion of how <form> elements might work in a map browsing context. We have had that discussion on and off in the MapML world e.g. <input type=location subtype=polygon> , but we need to actually implement something that experiments with ideas, to evaluate what's feasible. To do that, I believe we need to get some Web map developers from OpenLayers (for example), and/or OpenStreetMap etc., say, to help us with the user experience and so on.