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Why is there first an event called downloading while the progress events seem sufficient to determine everything? If we need downloading, wouldn't it be better to provide a networking API similar to media elements and XMLHttpRequest. I.e. with loadstart, progress, error/abort/load, and loadend?
'downloading' is separate from 'progress' so that you don't have to continually check whether or not you've gotten the first 'progress' yet. You just have one event to set up your progress bar (or whatever), and others to update it. The events you list aren't used because they're not fine-grained enough. What would be 'loadstart' is split between 'checking' and 'downloading', what would be the various ending events is split between 'noupdate', 'cached', 'updateready', 'obsolete', and 'error'. I reused the event names that made sense, and made new ones up elsewhere.