Sanitize @.delete|exists to define existence as being different from default

Author: lizmat

S32-setting-library/Containers.pod

@@ -687,18 +687,17 @@ Returns the length of the array counted in elements.
 
 =item delete
 
- method delete (@array : *@indices --> List ) is export
+ method delete (@array : Int $index --> $value ) is export
 
-Sets elements specified by C<@indices> in the invocant to a
-non-existent state, as if they never had a value. Deleted elements at
-the end of an Array shorten the length of the Array, unless doing so
-would violate an C<is shape()> definition.
+Sets the specified Array element to the default value of the Array.
 
-This is considered to be an internal method.  The interpretation of C<@indices>
-is therefor subject to change.  The normal way to delete is by applying a
-C<:delete> adverb to any subscripting operation.
+Deleted elements at the end of an Array shorten the length of the Array,
+unless doing so would violate an C<is shape()> definition.
 
-Returns the value(s) previously held in deleted locations.
+This is considered to be an internal method.  The normal way to delete is by
+applying a C<:delete> adverb to any subscripting operation.
+
+Returns the value previously held in deleted location.
 
 =item :delete
 
@@ -709,8 +708,8 @@ returns the elements normally, but reads them out destructively.
 
  method exists (@array: Int $index --> Bool )
 
-True if the specified Array element has been assigned to. This
-is not the same as being defined.
+True if the specified Array element has been assigned to with a value different
+from the default value of the Array.
 
 Supplying a different number of indices than invocant has dimensions is
 an error.