正确的方法是使用QSyntaxHighlighter，例如：

class MySyntaxHighlighter : public QSyntaxHighlighter {
public:
    MySyntaxHighlighter(QObject* parent) : QSyntaxHighlighter(parent)
    {
        KeywordsRed.push_back (
            QRegularExpression(
                "\\bred\\b",
                QRegularExpression::PatternOption::CaseInsensitiveOption
            )
        );
        KeywordsBold.push_back(
            QRegularExpression(
                "\\bbold\\b",
                QRegularExpression::PatternOption::CaseInsensitiveOption
            )
        );
    }
    virtual void highlightBlock(const QString& text) override
    {
        QTextCharFormat redFormat, boldFormat;
        redFormat.setForeground(QBrush(QColor::fromRgb(200, 0, 0)));
        if (auto textEdit = dynamic_cast<QTextEdit*>(parent()); textEdit) {
            QFont font = textEdit->font(); font.setBold(true);
            boldFormat.setFont(font);
        }
        for (const QRegularExpression& regexp : std::as_const(KeywordsRed)) {
            QRegularExpressionMatchIterator matchIterator = regexp.globalMatch(text);
            while (matchIterator.hasNext()) {
                QRegularExpressionMatch match = matchIterator.next();
                setFormat(match.capturedStart(), match.capturedLength(), redFormat);
            }
        }
        for (const QRegularExpression& regexp : std::as_const(KeywordsBold)) {
            QRegularExpressionMatchIterator matchIterator = regexp.globalMatch(text);
            while (matchIterator.hasNext()) {
                QRegularExpressionMatch match = matchIterator.next();
                setFormat(match.capturedStart(), match.capturedLength(), boldFormat);
            }
        }
    }
private:
    std::vector<QRegularExpression> KeywordsRed, KeywordsBold;
};

只需在QTextEdit上创建荧光笔即可附加荧光笔：

auto highlighter = new (std::nothrow) MySyntaxHighlighter(edit);