extend the standard context menu of qtextedit

[cai]

Hi all,
when i extend the standard context menu of qtextedit, i found all the actions is disable except the "paste" and "clear". why?

QMenu *editContextMenu = ui->textEdit->createStandardContextMenu();
    editContextMenu->addAction(clear);
    ui->textEdit->setContextMenuPolicy(Qt::CustomContextMenu);
    ...
    editContextMenu->exec(QCursor::pos());

QMenu *editContextMenu = ui->textEdit->createStandardContextMenu();
    editContextMenu->addAction(clear);
    ui->textEdit->setContextMenuPolicy(Qt::CustomContextMenu);
    ...
    editContextMenu->exec(QCursor::pos());

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