In one embodiment, a computing device may receive a structured document that includes a list of markers and place-marker elements corresponding to data objects of the structured document. Each marker in the list of markers corresponds to a subset of the place-marker elements. Without loading all the data objects, the device may determine a size of a scroll bar for a GUI based on size information associated with the place-marker elements. In response to detecting a scroll or resize event, an event handler may identify at least one marker in the list of markers whose corresponding subset of place-maker elements is within a portion of the structured document that is viewable through the graphical user interface. The handler may load the data objects corresponding to the subset of the place-marker elements corresponding to the identified marker. The identified marker may then be removed from the list of markers.