I would like to point out one thing that is not clear from the specification. In section 5.6 Browsing the Web(http://www.w3.org/TR/html5/browsers.html#browsing-the-web), if a user-agent is trying to grab a new HTML page that is not in cache (as per step 14 of the navigation algorithm) we will request to get that page using fetch algorithm(http://www.w3.org/TR/html5/infrastructure.html#fetch) which is executed in async mode. After initiating the request, the navigation algorithm in step 18 waits for few bytes to be available before moving on and the fetch algorithm is supposed to queue a task that will fill input byte stream and invoke html parser to do appropriate steps (http://www.w3.org/TR/html5/browsers.html#read-html). But HTML parser is created by queuing a task in step 23 of navigation algorithm. If fetch algorithm gets bytes before execution of step 23 how will it wait for creation of html parser? Will it spin the event loop?