As a footnote, there are cases that have interpreted this somewhat more broadly. We're dealing not only with alternative sources of information considered in relation to the source, but also with alternative sources of information considered in relation to the object. If one were videotaping a demonstration, it wouldn't be just alternative sources of the videotape; it would also be the information contained in the videotape. This gives rise to a host of other difficulties.
On March 5th, 2008. See this statement in context.