src/vs/workbench/contrib/webview/electron-browser/webviewElement.ts/ElectronWebviewBasedWebview/createElement
class ElectronWebviewBasedWebview:	protected createElement(options: WebviewOptions) {
		// Do not start loading the webview yet.
		// Wait the end of the ctor when all listeners have been hooked up.
		const element = document.createElement('webview');

		element.focus = () => {
			this.doFocus();
		};

		element.setAttribute('partition', webviewPartitionId);
		element.setAttribute('webpreferences', 'contextIsolation=yes');
		element.className = `webview ${options.customClasses || ''}`;

		element.style.flex = '0 1';
		element.style.width = '0';
		element.style.height = '0';
		element.style.outline = '0';

		return element;
	}