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Assuming nothing has been cached so far and you open the same URL twice, both URLs will start the "application cache update process". However, for whichever is second in starting this process (can it happen at the same time?) the master resource is no longer "new". (It still needs to be added to the list of pending master entries of course.) I suppose that dropping "new" would be enough if indeed they always happen after each other.
Checked in as WHATWG revision r4186. Check-in comment: Remove the word 'new' in 'new master entry' throughout the spec. http://html5.org/tools/web-apps-tracker?from=4185&to=4186