internal override XElement CreateXml()
{
var xRoot = new XElement(XmlConstants.Brick);
xRoot.SetAttributeValue(XmlConstants.Type, XmlConstants.XmlChangeVariableBrickType);
var xElement = VariableFormula.CreateXml();
xElement.SetAttributeValue(XmlConstants.Category, XmlConstants.VariableChange);
var xFormulalist = new XElement(XmlConstants.FormulaList);
xFormulalist.Add(xElement);
xRoot.Add(xFormulalist);
xRoot.Add(UserVariable.CreateXml());
return(xRoot);
}