LWG4060 submdspan preconditions do not forbid creating invalid pointer

Author: burblebee

source/containers.tex

@@ -23392,7 +23392,13 @@
 is \tcode{true}.
 
 \pnum
-Let \tcode{offset} be a value of type \tcode{size_t} equal to
+If \tcode{\exposid{first_}<index_type, $k$>(slices...)}
+equals \tcode{extents().extent($k$)}
+for any rank index $k$ of \tcode{extents()}, then
+let \tcode{offset} be a value of type \tcode{size_t} equal to
+\tcode{(*this).required_span_size()}.
+Otherwise,
+let \tcode{offset} be a value of type \tcode{size_t} equal to
 \tcode{(*this)(\exposid{first_}<index_type, P>(slices...)...)}.
 
 \rSec5[mdspan.sub.map.left]{\tcode{layout_left} specialization of \tcode{submdspan_mapping}}
@@ -23840,9 +23846,9 @@
 \effects
 Equivalent to:
 \begin{codeblock}
-auto sub_map_offset = submdspan_mapping(src.mapping(), slices...);
-return mdspan(src.accessor().offset(src.data(), sub_map_offset.offset),
-              sub_map_offset.mapping,
+auto sub_map_result = submdspan_mapping(src.mapping(), slices...);
+return mdspan(src.accessor().offset(src.data(), sub_map_result.offset),
+              sub_map_result.mapping,
               AccessorPolicy::offset_policy(src.accessor()));
 \end{codeblock}
 \end{itemdescr}