XmlElement读取为不区分大小写的C#

public class CaseInsensitiveXmlDocument : XmlDocument
{
    public override XmlElement CreateElement(string prefix, string localName, string namespaceURI)
    {
        return new CaseInsensitiveXmlElement(prefix, localName, namespaceURI, this);
    }
}

public class CaseInsensitiveXmlElement : XmlElement
{
    private CaseInsensitiveXmlDocument ownerDocument;

    public CaseInsensitiveXmlElement(string prefix, string localName, string namespaceURI, CaseInsensitiveXmlDocument ownerDocument)
        : base(prefix, localName, namespaceURI, ownerDocument)
    {
        this.ownerDocument = ownerDocument;
    }

    public override string LocalName
    {
        get { return base.LocalName.ToLower(); }
    }

    public override bool IsEqualNode(XmlNode node)
    {
        if (node is CaseInsensitiveXmlElement)
        {
            CaseInsensitiveXmlElement other = (CaseInsensitiveXmlElement)node;
            return string.Equals(this.LocalName, other.LocalName, StringComparison.OrdinalIgnoreCase);
        }
        return base.IsEqualNode(node);
    }
}

CaseInsensitiveXmlDocument doc = new CaseInsensitiveXmlDocument();
doc.Load("example.xml");

XmlElement element = doc.SelectSingleNode("/root/element") as XmlElement;