cpp/container/span/subspan

Obtains a span that is a view over the elements of this span starting at offset. If is std, the number of elements in the subspan is  (i.e., it ends at the end of ).

@1@ is ill-formed if
 * is greater than, or
 * is not std and is greater than.

The behavior is undefined if either or  is out of range. This happens if
 * is greater than size, or
 * is not std and is greater than.

The extent of the span returned by  is determined as follows:
 * If is not std, ;
 * Otherwise, if is not std, ;
 * Otherwise, std.

Return value
The requested subspan, such that. If is std, ; otherwise.