Minor fixes to blocking attributes

* Correct the IDL attribute declarations. Closes #7602.

* Improve the conformance requirements for blocking attributes to require that the tokens be "possible blocking tokens".

These were missed in f522f07 when blocking attributes were originally introduced.

source

@@ -7257,10 +7257,10 @@ a.setAttribute('href', 'https://example.com/'); // change the content attribute
   data-x="possible blocking token">possible blocking tokens</span>.</p>
 
   <p>A <span>blocking attribute</span> must have a value that is an <span>unordered set of unique
-  space-separated tokens</span>. The <span data-x="concept-supported-tokens">supported
-  tokens</span> of a <span>blocking attribute</span> are the <span data-x="possible blocking
-  token">possible blocking tokens</span>. Any element can have at most one <span>blocking
-  attribute</span>.</p>
+  space-separated tokens</span>, each of which are <span data-x="possible blocking token">possible
+  blocking tokens</span>. The <span data-x="concept-supported-tokens">supported tokens</span> of a
+  <span>blocking attribute</span> are the <span data-x="possible blocking token">possible blocking
+  tokens</span>. Any element can have at most one <span>blocking attribute</span>.</p>
 
   <p>The <dfn>blocking tokens set</dfn> for an element <var>el</var> are the result of the
   following steps:</p>
@@ -13651,7 +13651,7 @@ interface <dfn interface>HTMLLinkElement</dfn> : <span>HTMLElement</span> {
   [<span>CEReactions</span>] attribute USVString <span data-x="dom-link-imageSrcset">imageSrcset</span>;
   [<span>CEReactions</span>] attribute DOMString <span data-x="dom-link-imageSizes">imageSizes</span>;
   [<span>CEReactions</span>] attribute DOMString <span data-x="dom-link-referrerPolicy">referrerPolicy</span>;
-  [<span>CEReactions</span>] attribute DOMTokenList <span data-x="dom-link-blocking">blocking</span>;
+  [SameObject, PutForwards=<span data-x="dom-DOMTokenList-value">value</span>] readonly attribute <span>DOMTokenList</span> <span data-x="dom-link-blocking">blocking</span>;
   [<span>CEReactions</span>] attribute boolean <span data-x="dom-link-disabled">disabled</span>;
 
   // <a href="#HTMLLinkElement-partial">also has obsolete members</a>
@@ -15526,7 +15526,7 @@ interface <dfn interface>HTMLStyleElement</dfn> : <span>HTMLElement</span> {
   [<span>HTMLConstructor</span>] constructor();
 
   [<span>CEReactions</span>] attribute DOMString <span data-x="dom-style-media">media</span>;
-  [<span>CEReactions</span>] attribute DOMTokenList <span data-x="dom-style-blocking">blocking</span>;
+  [SameObject, PutForwards=<span data-x="dom-DOMTokenList-value">value</span>] readonly attribute <span>DOMTokenList</span> <span data-x="dom-style-blocking">blocking</span>;
 
   // <a href="#HTMLStyleElement-partial">also has obsolete members</a>
 };
@@ -58856,7 +58856,7 @@ interface <dfn interface>HTMLScriptElement</dfn> : <span>HTMLElement</span> {
   [<span>CEReactions</span>] attribute DOMString <span data-x="dom-script-text">text</span>;
   [<span>CEReactions</span>] attribute DOMString <span data-x="dom-script-integrity">integrity</span>;
   [<span>CEReactions</span>] attribute DOMString <span data-x="dom-script-referrerPolicy">referrerPolicy</span>;
-  [<span>CEReactions</span>] attribute DOMTokenList <span data-x="dom-script-blocking">blocking</span>;
+  [SameObject, PutForwards=<span data-x="dom-DOMTokenList-value">value</span>] readonly attribute <span>DOMTokenList</span> <span data-x="dom-script-blocking">blocking</span>;
 
   static boolean <span data-x="dom-script-supports">supports</span>(DOMString type);