WebKit iOS 15.0 Beta 1 to Beta 2 API Differences

WKWebView.h
Added -[WKWebView closeAllMediaPresentations:]
Added -[WKWebView pauseAllMediaPlayback:]
Added -[WKWebView resumeAllMediaPlayback:]
Added -[WKWebView suspendAllMediaPlayback:]
Added -[WKWebView requestMediaPlaybackState:]
Added WKWebView.underPageBackgroundColor