public void AddAttribute(XmlSchemaAttribute attribute)
        {
            string name = attribute.Name;

            if (name == null)
            {
                var ns = attribute.RefName.Namespace;
                if (string.IsNullOrEmpty(ns))
                {
                    return;
                }
                var prefix = nsMap.GetPrefix(ns);
                if (prefix == null)
                {
                    if (ns == "http://www.w3.org/XML/1998/namespace")
                    {
                        prefix = "xml";
                    }
                    else
                    {
                        return;
                    }
                }
                name = attribute.RefName.Name;
                if (prefix.Length > 0)
                {
                    name = prefix + ":" + name;
                }
            }
            if (!names.Add(name))
            {
                return;
            }
            string documentation = GetDocumentation(attribute.Annotation);

            Add(new XmlCompletionData(name, documentation, XmlCompletionData.DataType.XmlAttribute));
        }