1. A method comprising: receiving, by a content server from a client device, a first content item request for content for inclusion in a content item display environment of a resource hosted from a first network domain, the content item display environment hosted from a second network domain different from the first network domain; providing, by the content server, responsive to receiving the first content item request, a first content item and instructions causing the client device to generate a child display environment of the content item display environment by interacting with a publisher side file hosted by a device in the first network domain, the instructions further causing the client device to transmit a parameterized request from the client device to the device in the first network domain, the parameterized request passing parameters to access configuration determination instructions that cause the client device to generate, using the child display environment, measurement data for the resource and for the content item display environment; receiving, from the client device, the generated measurement data specifying a configuration of the content item display environment and the resource; determining that a position of the content item display environment permits an expandable advertisement to be expanded without intersecting a boundary of the resource; receiving, by the content server, a second content item request for content to display in the content item display environment, the second content item request received subsequent to the first content item request; selecting, by the content server, a second content item from a plurality of second content items based at least in part on the measurement data, and based at least on the determination that a position of the content item display environment permits an expandable advertisement to be expanded without intersecting a boundary of the resource, wherein the second content item is an expandable advertisement; and providing, by a content server, data specifying the selected second content item responsive to the second content item request, the data specifying the selected second content item causing the client device to display the selected second content item.