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void QTextControlPrivate::setContent(Qt::TextFormat format, const QString &text, QTextDocument *document)
{
    Q_Q(QTextControl);

    // for use when called from setPlainText. we may want to re-use the currently
    // set char format then.
    const QTextCharFormat charFormatForInsertion = cursor.charFormat();

    bool clearDocument = true;
    if (!doc) {
        if (document) {
            doc = document;
            clearDocument = false;
        } else {
            palette = QApplication::palette("QTextControl");
// QTextDocument *doc; - приватный член класса QTextControl
///------------------------------------------------------------

            doc = new QTextDocument(q);

///------------------------------------------------------------

        }
        _q_documentLayoutChanged();
        cursor = QTextCursor(doc);

// ####        doc->documentLayout()->setPaintDevice(viewport);

        QObject::connect(doc, SIGNAL(contentsChanged()), q, SLOT(_q_updateCurrentCharFormatAndSelection()));
        QObject::connect(doc, SIGNAL(cursorPositionChanged(QTextCursor)), q, SLOT(_q_emitCursorPosChanged(QTextCursor)));
        QObject::connect(doc, SIGNAL(documentLayoutChanged()), q, SLOT(_q_documentLayoutChanged()));

        // convenience signal forwards
        QObject::connect(doc, SIGNAL(undoAvailable(bool)), q, SIGNAL(undoAvailable(bool)));
        QObject::connect(doc, SIGNAL(redoAvailable(bool)), q, SIGNAL(redoAvailable(bool)));
        QObject::connect(doc, SIGNAL(modificationChanged(bool)), q, SIGNAL(modificationChanged(bool)));
        QObject::connect(doc, SIGNAL(blockCountChanged(int)), q, SIGNAL(blockCountChanged(int)));
    }

    bool previousUndoRedoState = doc->isUndoRedoEnabled();
    if (!document)
        doc->setUndoRedoEnabled(false);

    //Saving the index save some time.
    static int contentsChangedIndex = QTextDocument::staticMetaObject.indexOfSignal("contentsChanged()");
    static int textChangedIndex = QTextControl::staticMetaObject.indexOfSignal("textChanged()");
    // avoid multiple textChanged() signals being emitted
    QMetaObject::disconnect(doc, contentsChangedIndex, q, textChangedIndex);

    if (!text.isEmpty()) {
        // clear 'our' cursor for insertion to prevent
        // the emission of the cursorPositionChanged() signal.
        // instead we emit it only once at the end instead of
        // at the end of the document after loading and when
        // positioning the cursor again to the start of the
        // document.
        cursor = QTextCursor();
        if (format == Qt::PlainText) {
            QTextCursor formatCursor(doc);
            // put the setPlainText and the setCharFormat into one edit block,
            // so that the syntax highlight triggers only /once/ for the entire
            // document, not twice.
            formatCursor.beginEditBlock();
            doc->setPlainText(text);
            doc->setUndoRedoEnabled(false);
            formatCursor.select(QTextCursor::Document);
            formatCursor.setCharFormat(charFormatForInsertion);
            formatCursor.endEditBlock();
        } else {
#ifndef QT_NO_TEXTHTMLPARSER
            doc->setHtml(text);
#else
            doc->setPlainText(text);
#endif
            doc->setUndoRedoEnabled(false);
        }
        cursor = QTextCursor(doc);
    } else if (clearDocument) {
        doc->clear();
    }
    cursor.setCharFormat(charFormatForInsertion);

    QMetaObject::connect(doc, contentsChangedIndex, q, textChangedIndex);
    emit q->textChanged();
    if (!document)
        doc->setUndoRedoEnabled(previousUndoRedoState);
    _q_updateCurrentCharFormatAndSelection();
    if (!document)
        doc->setModified(false);

    q->ensureCursorVisible();
    emit q->cursorPositionChanged();
}

void QTextControl::clear()
{
    Q_D(QTextControl);
    // clears and sets empty content
    d->extraSelections.clear();
    d->setContent();
}