System.Xml.XmlTextWriter.VerifyPrefixXml C# (CSharp) Method

        void VerifyPrefixXml(string prefix, string ns) {

            if (prefix != null && prefix.Length == 3) {
                if (
                   (prefix[0] == 'x' || prefix[0] == 'X') &&
                   (prefix[1] == 'm' || prefix[1] == 'M') &&
                   (prefix[2] == 'l' || prefix[2] == 'L')
                   ) {
                    if (XmlReservedNs.NsXml != ns) {
                        throw new ArgumentException(Res.GetString(Res.Xml_InvalidPrefix));
                    }
                }
            }
        }