A correction and a simplification

Author: encukou

Doc/reference/datamodel.rst

@@ -323,8 +323,8 @@ Sequences also support slicing: ``a[start:stop]`` selects all items with index *
 that *start* ``<=`` *k* ``<`` *stop*.  When used as an expression, a slice is a
 sequence of the same type. The comment above about negative subscripts also applies
 to negative slice positions.
-Note that no error is raised if a slice positions is larger than the length
-of the sequence.
+Note that no error is raised if a slice position is less than zero or larger
+than the length of the sequence.
 
 If *start* is missing or ``None``, slicing behaves as if *start* was zero.
 If *stop* is missing or ``None``, slicing behaves as if *stop* was equal to

Doc/reference/expressions.rst

@@ -1120,10 +1120,7 @@ Formal subscription grammar
    subscript:    `slice` | `tuple_slices`
    tuple_slices: ','.(`slice` | `starred_expression`)+ [',']
    slice:        `proper_slice` | `assignment_expression`
-   proper_slice: [`lower_bound`] ":" [`upper_bound`] [ ":" [`stride`] ]
-   lower_bound:  `expression`
-   upper_bound:  `expression`
-   stride:       `expression`
+   proper_slice: [`expression`] ":" [`expression`] [ ":" [`expression`] ]
 
 There is a semantic difference between the alternatives for *subscript*.
 If *subscript* contains ony one unstarred *slice* without a trailing comma,