System.Xml.Schema.XmlAtomicValue.GetPrefixFromQName C# (CSharp) Method

        private string GetPrefixFromQName(string value) {
            int colonOffset;
            int len = ValidateNames.ParseQName(value, 0, out colonOffset);

            if (len == 0 || len != value.Length) {
                return null;
            }
            if (colonOffset != 0) {
                return value.Substring(0, colonOffset);
            }
            else {
                return string.Empty;
            }
        }
    }