This is used to look for relationships between site and event especially for endoscopy events where sentences such as 'The stomach polyp was large. It was removed with a snare' ie the therapy and the site are in two different locations.
See also
Other Basic Column mutators:
EntityPairs_OneSentence()
,
ExtrapolatefromDictionary()
,
ListLookup()
,
MyImgLibrary()