"Most" not "Some" seq. do implement negative index.

Author: Alex-Wasowicz

Doc/reference/datamodel.rst

@@ -308,7 +308,7 @@ Sequences
 These represent finite ordered sets indexed by non-negative numbers. The
 built-in function :func:`len` returns the number of items of a sequence. When
 the length of a sequence is *n*, the index set contains the numbers 0, 1,
-..., *n*-1.  Item *i* of sequence *a* is selected by ``a[i]``. Some sequences,
+..., *n*-1.  Item *i* of sequence *a* is selected by ``a[i]``. Most sequences,
 including built-in sequences, interpret negative subscripts by adding the
 sequence length. For example, ``a[-2]`` equals ``a[n-2]``, the second to last
 item of sequence a with length ``n``.