Normative: toSorted methods must be stable (tc39#3424)

spec.html

@@ -39805,6 +39805,9 @@ <h1>
             <li>
               Then for all non-negative integers _j_ and _k_, each less than _itemCount_, if <emu-eqn>ℝ(_SortCompare_(old[_j_], old[_k_])) &lt; 0</emu-eqn>, then <emu-eqn>π(_j_) &lt; π(_k_)</emu-eqn>.
             </li>
+            <li>
+              And for all non-negative integers _j_ and _k_ such that _j_ &lt; _k_ &lt; _itemCount_, if <emu-eqn>ℝ(_SortCompare_(old[_j_], old[_k_])) = 0</emu-eqn>, then <emu-eqn>π(_j_) &lt; π(_k_)</emu-eqn>; i.e., the sort is stable.
+            </li>
           </ul>
           <p>Here the notation <emu-eqn>old[_j_]</emu-eqn> is used to refer to <emu-eqn>_items_[_j_]</emu-eqn> before step <emu-xref href="#step-array-sort"></emu-xref> is executed, and the notation <emu-eqn>new[_j_]</emu-eqn> to refer to <emu-eqn>_items_[_j_]</emu-eqn> after step <emu-xref href="#step-array-sort"></emu-xref> has been executed.</p>
           <p>An abstract closure or function _comparator_ is a <dfn id="consistent-comparator">consistent comparator</dfn> for a set of values _S_ if all of the requirements below are met for all values _a_, _b_, and _c_ (possibly the same value) in the set _S_: The notation <emu-eqn>_a_ &lt;<sub>C</sub> _b_</emu-eqn> means <emu-eqn>ℝ(_comparator_(_a_, _b_)) &lt; 0</emu-eqn>; <emu-eqn>_a_ =<sub>C</sub> _b_</emu-eqn> means <emu-eqn>ℝ(_comparator_(_a_, _b_)) = 0</emu-eqn>; and <emu-eqn>_a_ ><sub>C</sub> _b_</emu-eqn> means <emu-eqn>ℝ(_comparator_(_a_, _b_)) > 0</emu-eqn>.</p>