How to use qwebkitplatformplugin?

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how to use qwebkitplatformplugin in a QWebView?

I have the following code:

#include <QWebKitPlatformPlugin>
 
MainWindow::MainWindow(QWidget *parent, bool new) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
 
    webView = new QWebView;
    ui->webViewLay->addWidget(webView);
    webView->setHtml("<p>test</p>");
}

#include <QWebKitPlatformPlugin>
 
MainWindow::MainWindow(QWidget *parent, bool new) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
 
    webView = new QWebView;
    ui->webViewLay->addWidget(webView);
    webView->setHtml("<p>test</p>");
}

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but found no example of how to use extensions.