message: Combine multiple paragraphs into one in docstring, based on review feedback
diff: @@ -40,9 +40,7 @@ For each string in the input `Tensor`, creates a substring starting at index
  `pos` with a total length of `len`.
  If `len` defines a substring that would extend beyond the length of the input
  -string, then as many characters as possible are used.
  -
  -A negative `len` indicates all characters until the end of the string.
  +string, or if `len` is negative, then as many characters as possible are used.
  A negative `pos` indicates distance within the string backwards from the end.
  