有没有办法同时搜索两个FlowDocuments？

// 创建两个FlowDocument
FlowDocument document1 = new FlowDocument();
FlowDocument document2 = new FlowDocument();

// 在两个FlowDocument中添加内容

// 创建两个FlowDocumentScrollViewer
FlowDocumentScrollViewer viewer1 = new FlowDocumentScrollViewer();
FlowDocumentScrollViewer viewer2 = new FlowDocumentScrollViewer();

// 将FlowDocuments分别放置在两个FlowDocumentScrollViewer中
viewer1.Document = document1;
viewer2.Document = document2;

// 创建一个搜索框
TextBox searchBox = new TextBox();

// 监听搜索框的文本变化事件
searchBox.TextChanged += (sender, e) =>
{
    string keyword = searchBox.Text;

    // 在两个FlowDocuments中搜索关键字并进行相应操作
    // ...

    // 示例：标记匹配的文本
    TextRange range1 = new TextRange(document1.ContentStart, document1.ContentEnd);
    TextRange range2 = new TextRange(document2.ContentStart, document2.ContentEnd);

    range1.ClearAllProperties();
    range2.ClearAllProperties();

    TextPointer pointer1 = range1.Start;
    TextPointer pointer2 = range2.Start;

    while (pointer1 != null)
    {
        string text = pointer1.GetTextInRun(LogicalDirection.Forward);
        int index = text.IndexOf(keyword);

        if (index >= 0)
        {
            TextPointer start = pointer1.GetPositionAtOffset(index);
            TextPointer end = start.GetPositionAtOffset(keyword.Length);

            range1.ApplyPropertyValue(TextElement.BackgroundProperty, Brushes.Yellow);
            range1.ApplyPropertyValue(TextElement.ForegroundProperty, Brushes.Black);
            range1.ApplyPropertyValue(TextElement.FontWeightProperty, FontWeights.Bold);
            range1.ApplyPropertyValue(TextElement.FontSizeProperty, 14.0);

            range1 = new TextRange(end, range1.End);
            pointer1 = end;
        }
        else
        {
            pointer1 = pointer1.GetNextContextPosition(LogicalDirection.Forward);
        }
    }

    while (pointer2 != null)
    {
        string text = pointer2.GetTextInRun(LogicalDirection.Forward);
        int index = text.IndexOf(keyword);

        if (index >= 0)
        {
            TextPointer start = pointer2.GetPositionAtOffset(index);
            TextPointer end = start.GetPositionAtOffset(keyword.Length);

            range2.ApplyPropertyValue(TextElement.BackgroundProperty, Brushes.Yellow);
            range2.ApplyPropertyValue(TextElement.ForegroundProperty, Brushes.Black);
            range2.ApplyPropertyValue(TextElement.FontWeightProperty, FontWeights.Bold);
            range2.ApplyPropertyValue(TextElement.FontSizeProperty, 14.0);

            range2 = new TextRange(end, range2.End);
            pointer2 = end;
        }
        else
        {
            pointer2 = pointer2.GetNextContextPosition(LogicalDirection.Forward);
        }
    }
};

// 创建一个包含两个FlowDocumentScrollViewer和搜索框的界面布局
// ...