Editorial: add an ID to the "property key" dfn

spec.html

@@ -2739,7 +2739,7 @@ <h1>The Object Type</h1>
           An <dfn variants="accessor properties">accessor property</dfn> associates a key value with one or two accessor functions, and a set of Boolean attributes. The accessor functions are used to store or retrieve an ECMAScript language value that is associated with the property.
         </li>
       </ul>
-      <p>The properties of an object are uniquely identified using property keys. A <dfn variants="property keys" oldids="sec-ispropertykey">property key</dfn> is either a String or a Symbol. All Strings and Symbols, including the empty String, are valid as property keys. A <dfn id="property-name">property name</dfn> is a property key that is a String.</p>
+      <p>The properties of an object are uniquely identified using property keys. A <dfn id="property-key" variants="property keys" oldids="sec-ispropertykey">property key</dfn> is either a String or a Symbol. All Strings and Symbols, including the empty String, are valid as property keys. A <dfn id="property-name">property name</dfn> is a property key that is a String.</p>
       <p>An <dfn id="integer-index" variants="integer indices,integer-indexed">integer index</dfn> is a property name _n_ such that CanonicalNumericIndexString(_n_) returns an integral Number in the inclusive interval from *+0*<sub>𝔽</sub> to 𝔽(2<sup>53</sup> - 1). An <dfn id="array-index" variants="array indices">array index</dfn> is an integer index _n_ such that CanonicalNumericIndexString(_n_) returns an integral Number in the inclusive interval from *+0*<sub>𝔽</sub> to 𝔽(2<sup>32</sup> - 2).</p>
       <emu-note>
         <p>Every non-negative safe integer has a corresponding integer index. Every 32-bit unsigned integer except <emu-eqn>2<sup>32</sup> - 1</emu-eqn> has a corresponding array index. *"-0"* is neither an integer index nor an array index.</p>