add cloning here instead

storage.bs

@@ -228,6 +228,28 @@ It is initially empty.
 browsing session. It is roughly analogous to <a>top-level browsing context</a> except that it cannot
 be replaced due to <code>Cross-Origin-Opener-Policy</code> or navigation.
 
+<p>To <dfn export>legacy-clone a browsing session storage shed</dfn>, given a browsing session
+<var>A</var> and a browsing session <var>B</var>, run these steps:
+
+<ol>
+ <li>
+  <p><a for=map>For each</a> <var>key</var> → <var>shelf</var> of <var>A</var>'s
+  <a for="browsing session">storage shed</a>:
+
+  <ol>
+   <li><p>Let <var>newShelf</var> be the result of running <a>create a storage shelf</a> with
+   "<code>session</code>".
+
+   <li><p>Set <var>newShelf</var>'s <a>bucket map</a>["<code>default</code>"]'s
+   <a>bottle map</a>["<code>sessionStorage</code>"]'s <a for="storage bottle">map</a> to a
+   <a for=map>clone</a> of <var>shelf</var>'s <a>bucket map</a>["<code>default</code>"]'s
+   <a>bottle map</a>["<code>sessionStorage</code>"]'s <a for="storage bottle">map</a>.
+
+   <li><p>Set <var>B</var>'s <a for="browsing session">storage shed</a>[<var>key</var>] to
+   <var>newShelf</var>.
+  </ol>
+</ol>
+
 
 <h3 id=storage-shelves>Storage shelves</h3>
 
@@ -261,8 +283,8 @@ given a <a for=map>value</a> when a <a>storage shelf</a> is
 <var>environment</var>, return the result of running <a>obtain a storage shelf</a> with the user
 agent's <a for="user agent">storage shed</a>, <var>environment</var>, and "<code>local</code>".
 
-<p>To <dfn export>create a storage shelf</dfn>, given a <a>storage type</a> <var>type</var>, run
-these steps:
+<p>To <dfn>create a storage shelf</dfn>, given a <a>storage type</a> <var>type</var>, run these
+steps:
 
 <ol>
  <li><p>Let <var>shelf</var> be a new <a>storage shelf</a>.