20. The system of claim 19 , wherein the identified set of documents does not include the first document, does not include the second document, and does include the third, fourth, fifth, and sixth documents.
21. The system of claim 20 , wherein the term index is generated based on the plurality of documents, wherein the overlay index is generated based on the specified context and the term index, wherein documents including the first search term are identified using the overlay index if the first search term is included in the specified context and using the term index if the first search term is not included in the specified context.