14. A system, comprising: one or more computers and one or more storage devices storing instructions that are operable, when executed by the one or more computers, to cause the one or more computers to perform operations comprising: obtaining identity information, with a portable program module, for a source of a webpage associated with a container document, the portable program module located in the container document; submitting, by the portable program module located in the container document, the identity information to a concept server storing keywords associated with the container document; receiving, by the portable program module located on the container document and from the concept server, in response to the submitted identity information, the keywords associated with the container document; selecting, by the portable program module located in the container document, a subset of the keywords received from the concept server based at least on one or more criteria specified by an author of the portable program module; submitting, by the portable program module located in the container document, a query to an item search server related to the subset of the keywords selected by the portable program module; and receiving, at the portable program module located in the container document, advertisements responsive to the query from the item search server for display.
20. The system of claim 14 , wherein the identity information for a source of a webpage comprises a URL associated with the container document.