17. The system of claim 4 , wherein the first selection input also selects a selected subset of the first set of one or more response snippets that is nonempty, and the first matching document snippet is canonically similar to the selected subset of the first set of one or more response snippets.
17. The system of claim 4 , wherein the first selection input also selects a selected subset of the first set of one or more response snippets that is nonempty, and the first matching document snippet is canonically similar to the selected subset of the first set of one or more response snippets. 18. The system of claim 17 , wherein the selected subset comprises all of the snippets of the first set of one or more response snippets.