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The web browser object uses an Apple class called WebView. Apple has now replaced this with a new class called WKWebView. On iOS they have discontinued WebView, but for now macOS contains both of these classes. I think this is because WKWebView does not include all of the features that WebView has, and some popular web authoring apps will completely break if WebView is discontinued. WKWebView uses a somewhat different communication interface from WebView. Apple has stated that they plan to discontinue WebView, but so far has not made any move to add the additional features to WKWebView. So the future on this topic is rather cloudy.