[css-view-transitions-2] Make some syntax clarifications (#10158)

- Add [SameObject] to CSSOM
- Clarify that classes can't include white space

css-view-transitions-2/Overview.bs

@@ -449,7 +449,7 @@ The {{CSSViewTransitionRule}} represents a ''@view-transition'' rule.
  [Exposed=Window]
  interface CSSViewTransitionRule : CSSRule {
  readonly attribute ViewTransitionNavigation navigation;
- readonly attribute FrozenArray<CSSOMString> types;
+ [SameObject] readonly attribute FrozenArray<CSSOMString> types;
  };
 </xmp>
 
@@ -675,10 +675,15 @@ div.box {
  <<pt-name-and-class-selector>> has the following syntax definition:
 
  <pre class=prod>
- <dfn>&lt;pt-name-and-class-selector></dfn> = <<pt-name-selector>><<pt-class-selector>>? | <<pt-class-selector>>
+ <dfn>&lt;pt-name-and-class-selector></dfn> = <<pt-name-selector>> <<pt-class-selector>>? | <<pt-class-selector>>
  <dfn>&lt;pt-class-selector></dfn> = ['.' <<custom-ident>>]+
  </pre>
 
+ When interpreting the above grammar, white space is forbidden:
+
+ * Between <<pt-name-selector>> and <<pt-class-selector>>
+ * Between any of the components of <<pt-class-selector>>.
+
  A [=named view transition pseudo-element=] [=selector=] which has one or more <<custom-ident>> values
  in its <<pt-class-selector>> would only match an element if the [=captured element/class list=] value in
  [=ViewTransition/named elements=] for the pseudo-element's 'view-transition-name' [=list/contains=] all of those values.