XmlReaderExtensions

Reader.cs

if (!reader.MoveToNextElement(0) || (reader.Name != "Root"))
{
    return;
}

while (reader.MoveToNextElement(1))
{
    if (reader.Name == "Group1")
    {
        while (reader.MoveToNextElement(2))
        {
            // <Root><Group1>...</Group1></Root>内の要素の処理
        }
    }
    else if (reader.Name == "Group2")
    {
        while (reader.MoveToNextElement(2))
        {
            // <Root><Group2>...</Group2></Root>内の要素の処理
        }
    }
}

XmlReaderExtensions.cs

public static class XmlReaderExtensions
{
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static bool MoveToNextElement(this XmlReader reader, int depth)
    {
        while (reader.Read())
        {
            if ((reader.NodeType == XmlNodeType.Element) && (reader.Depth == depth))
            {
                return true;
            }
    
            if (reader.Depth < depth)
            {
                return false;
            }
        }
    
        return false;
    }
}