Add notes for steps that mirror ECMAScript

Author: MattiasBuelens

index.bs

@@ -9324,6 +9324,11 @@ a reference to the same object that the IDL value represents.
     1.  Let |jsView| be the result of [=converted to a JavaScript value|converting=] |view| to
         a JavaScript value.
     1.  Return |jsView|.\[[ByteOffset]].
+
+    <p class="note">These steps are equivalent to
+    {{%TypedArray%/byteOffset|%TypedArray%.prototype.byteOffset}} (for a
+    [=typed array type=] instance) or {{DataView/byteOffset|DataView.prototype.byteOffset}}
+    (for a {{DataView}}).
 </div>
 
 <div algorithm>
@@ -9339,17 +9344,24 @@ a reference to the same object that the IDL value represents.
                 Seq-Cst).
             1.  If [$IsTypedArrayOutOfBounds$](|taRecord|) is true, then return 0.
             1.  Return [$TypedArrayByteLength$](|taRecord|).
+                <p class="note">The above substeps are equivalent to
+                {{%TypedArray%/byteLength|%TypedArray%.prototype.byteLength}}.
         1.  Otherwise:
             1.  [=/Assert=]: |jsBufferSource| is a {{DataView}}.
             1.  Let |viewRecord| be [$MakeDataViewWithBufferWitnessRecord$](|jsBufferSource|,
                 Seq-Cst).
             1.  If [$IsViewOutOfBounds$](|viewRecord|) is true, then [=JavaScript/throw=] a
                 <l spec=ecmascript>{{TypeError}}</l>.
             1.  Return [$GetViewByteLength$](|viewRecord|).
+                <p class="note">The above substeps are equivalent to
+                {{DataView/byteLength|DataView.prototype.byteLength}}.
     1.  Otherwise:
         1.  [=/Assert=]: |jsBufferSource| is an {{ArrayBuffer}} or a {{SharedArrayBuffer}}.
         1.  If [$IsDetachedBuffer$](|jsBufferSource|) is true, then return 0.
         1.  Return [$ArrayBufferByteLength$](|jsBufferSource|, Seq-Cst).
+            <p class="note">The above substeps are equivalent to
+            {{ArrayBuffer/byteLength|ArrayBuffer.prototype.byteLength}} or
+            {{SharedArrayBuffer/byteLength|SharedArrayBuffer.prototype.byteLength}}.
 </div>
 <!-- TODO: should this be stricter around not being detached? -->