"Update the rendering" should specify what happens when a Document becomes rendering blocking during a "update the rendering"

[mrobinson]

What is the issue with the HTML Standard?

https://html.spec.whatwg.org/multipage/webappapis.html#update-the-rendering filters documents just once in step 3:

Filter non-renderable documents: Remove from docs any Document object doc for which any of the following are true:

• doc is render-blocked;
• doc's visibility state is "hidden";
• doc's rendering is suppressed for view transitions; or
• doc's node navigable doesn't currently have a rendering opportunity.

A document may also become render blocking while later steps happen in the procedure such as requestAnimationFrame callbacks. The specification should say what happens in this case when this occurs. I believe that in this case, Firefox does not update the rendering: https://searchfox.org/firefox-main/rev/7f94689f2c228a96f6c271e30880e72778b7ab15/layout/base/nsRefreshDriver.cpp#2637