Problem is solved by add new function:
function GetVarVal(aValue: TXmlString): Variant;
This function is used in
procedure TXmlNode.SetAttr(const aName, aValue: TXmlString);
and
procedure TXmlNode.SetAttr(aNameID: Integer; const aValue: TXmlString);
Signed-off-by: Andrey Matveev <dvorkin.zilog@gmail.com>