Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for locating, using a content binder library, content elements of a publisher page. For each content element, the library determines presentation attributes of the content element and at least one other library detects a mode parameter that specifies a type of user device that is requesting the publisher page. The library selects a particular content element from the publisher page as a reference point for positioning a digital component at the publisher page using the presentation attributes of the particular content element. The library determines a location of the publisher page for rendering the digital component, where the location is determined based on the reference point and the mode parameter. The library provides the digital component for display at the location of the publisher page.