One or more servers can implement a method including generating an information resource comprising a content package including first content, metadata of a content extension, and a script for displaying the first content, and transmitting the information resource to a client device to cause the client device to: display the first content within an inline frame; identify an interaction with a user interface feature; transmit, responsive to identifying the interaction, a content extension request based on the metadata of the content extension; receive, responsive to the content extension request, a second content item; responsive to identifying the interaction, expand the inline frame from the first size to a second size; and display, in the expanded inline frame, the second content item, the second content item different from the first content item.