18. The media of claim 17 , wherein: when the event comprises selection of a link rendered or embedded within the first structured document, extracting the URL for the second structured document comprises: examining one or more link attributes associated with the link; and extracting the target URL from the one or more link attributes; and when the event comprises input causing forward or backward navigation from the first structured document, extracting the URL for the second structured document comprises: examining a data store of a history manager executing in connection with the client application; and extracting the URL from the data store.
17. The media of claim 15 , wherein the software is further operable when executed to extract a Uniform Resource Locator (URL) for the second structured document.