· Import from compat what comes from compat. Yes, some names are available in utils too, but that's an implementation detail.
· Use _match_id consistently whenever possible
· Fix some outdated tests
· Use consistent valid URL (always match the whole protocol, no ^ at start required)
· Use modern test definitions
A suitable downloader can be found using the 'get_suitable_downloader' function.
Each subclass implements 'real_download', for downloading an info dict you call the 'download' method, which first checks if the video has already been downloaded
