Editorial: Split identity into spec and language identity

This 2-level stratification of identity is needed rigor for Symbols as
WeakMap keys (tc39#2777) to capture the reason for why Symbol.for symbols
cannot be used as weak targets.

spec.html

@@ -1085,10 +1085,10 @@ <h1>Value Notation</h1>
 
     <emu-clause id="sec-identity">
       <h1>Identity</h1>
-      <p>In this specification, the word “is” is used to compare two values through equality, as in “If _bool_ is *true*, then”. For the purposes of this equality comparison, all values within this specification fall into one of the following two categories.</p>
-      <p><dfn variants="values without identity,value without identity">Values without identity</dfn> are equal to other values without identity if all of their innate characteristics are the same — characteristics such as the magnitude of an integer or the length of a sequence. Because of this, values without identity may be manifest anywhere simply by fully describing their characteristics. It is not meaningful to change the characteristics of a value that does not have identity. Examples of values without identity include, but are not limited to: <emu-xref href="#sec-ecmascript-language-types-boolean-type">Booleans</emu-xref>; mathematical values and extended mathematical values; <emu-xref href="#sec-ecmascript-language-types-number-type">Numbers</emu-xref>; <emu-xref href="#sec-ecmascript-language-types-bigint-type">BigInts</emu-xref>; *null*; *undefined*; sequences, including <emu-xref href="#sec-ecmascript-language-types-string-type">Strings</emu-xref>, ECMAScript source text, surrogate pairs, Directive Prologues, etc; UTF-16 code units; Unicode code points; enums; abstract operations, including syntax-directed operations, host hooks, etc; and ordered pairs. The preceding list is exhaustive for ECMAScript language values.</p>
-      <p>In contrast, each <dfn variants="values with identity">value with identity</dfn> is unique and therefore only equal to itself. Values with identity are like values without identity but with an additional unguessable, unchangeable, universally-unique characteristic called <em>identity</em>. References to existing values with identity cannot be manifest simply by describing them, as the identity itself is indescribable; instead, references to these values must be explicitly passed from one place to another. Some values with identity are mutable and therefore can have their characteristics (except their identity) changed in-place, causing all holders of the value to observe the new characteristics. Examples of values with identity include, but are not limited to: <emu-xref href="#sec-object-type">Objects</emu-xref>, including function objects, exotic objects, etc; any kind of Records, including Property Descriptors, PrivateElements, etc; <emu-xref href="#sec-ecmascript-language-types-symbol-type">symbols</emu-xref>; Parse Nodes; Lists; <emu-xref href="#sec-set-and-relation-specification-type">Sets</emu-xref> and Relations; Abstract Closures; Data Blocks; Private Names; execution contexts and execution context stacks; agent signifiers; and WaiterLists. The preceding list is exhaustive for ECMAScript language values.</p>
-      <p>A value without identity is never equal to a value with identity.</p>
+      <p>In this specification, both specification values and ECMAScript language values are compared to each other for equality. When comparing equality, values fall into one of two categories. <dfn variants="values without identity,value without identity">Values without identity</dfn> are equal to other values without identity if all of their innate characteristics are the same — characteristics such as the magnitude of an integer or the length of a sequence. Values without identity may be manifest without prior reference by fully describing their characteristics. In contrast, each <dfn variants="values with identity">value with identity</dfn> is unique and therefore only equal to itself. Values with identity are like values without identity but with an additional unguessable, unchangeable, universally-unique characteristic called <em>identity</em>. References to existing values with identity cannot be manifest simply by describing them, as the identity itself is indescribable; instead, references to these values must be explicitly passed from one place to another. Some values with identity are mutable and therefore can have their characteristics (except their identity) changed in-place, causing all holders of the value to observe the new characteristics. A value without identity is never equal to a value with identity.</p>
+      <p>From the perspective of this specification, the word “is” is used to compare two values for equality, as in “If _bool_ is *true*, then ...”, and the word “contains” is used to search for a value inside lists using equality comparisons, as in "If _list_ contains a Record _r_ such that _r_.[[Foo]] is *true*, then ...". From the perspective of the ECMAScript language, language values are compared for quality using the SameValue abstract operation and the abstract operations it transitively calls.</p>
+      <p>For specification values, examples of values without identity include, but are not limited to: mathematical values and extended mathematical values; ECMAScript source text, surrogate pairs, Directive Prologues, etc; UTF-16 code units; Unicode code points; enums; abstract operations, including syntax-directed operations, host hooks, etc; and ordered pairs. Examples of specification values with identity include, but are not limited to: any kind of Records, including Property Descriptors, PrivateElements, etc; Parse Nodes; Lists; <emu-xref href="#sec-set-and-relation-specification-type">Sets</emu-xref> and Relations; Abstract Closures; Data Blocks; Private Names; execution contexts and execution context stacks; agent signifiers; and WaiterLists. These lists are not exhaustive.</p>
+      <p>ECMAScript language values without identity are <emu-xref href="#sec-ecmascript-language-types-undefined-type">*undefined*</emu-xref>, <emu-xref href="#sec-ecmascript-language-types-null-type">*null*</emu-xref>, <emu-xref href="#sec-ecmascript-language-types-boolean-type">Booleans</emu-xref>, <emu-xref href="#sec-ecmascript-language-types-string-type">String</emu-xref>, <emu-xref href="#sec-ecmascript-language-types-number-type">Numbers</emu-xref>, and <emu-xref href="#sec-ecmascript-language-types-bigint-type">BigInts</emu-xref>. ECMAScript language values with identity are <emu-xref href="#sec-ecmascript-language-types-symbol-type">Symbols</emu-xref> and <emu-xref href="#sec-object-type">Objects</emu-xref>. Note that Symbols produced by <emu-xref href="#sec-symbol.for">Symbol.for</emu-xref> are a special case; they have identity from the perspective of the specification but do not have identity from the perspective of the ECMAScript language. These lists are exhaustive.</p>
     </emu-clause>
   </emu-clause>
 </emu-clause>