diff --git a/xmind/core/const.py b/xmind/core/const.py
index a9b27d1..a1b0bcb 100644
--- a/xmind/core/const.py
+++ b/xmind/core/const.py
@@ -55,6 +55,7 @@
 ATTR_END1 = "end1"
 ATTR_END2 = "end2"
 ATTR_MARKERID = "marker-id"
+ATTR_STRUCTURE ="structure-class"
 
 NS_URI = "http://www.w3.org/1999/xhtml"
 
diff --git a/xmind/core/topic.py b/xmind/core/topic.py
index 9b011cd..adef2dd 100644
--- a/xmind/core/topic.py
+++ b/xmind/core/topic.py
@@ -62,6 +62,12 @@ def _get_children(self):
     def _set_hyperlink(self, hyperlink):
         self.setAttribute(const.ATTR_HREF, hyperlink)
         #self.updateModifiedTime()
+       
+    def _set_structure(self,structure):
+        self.setAttribute(const.ATTR_STRUCTURE,structure)  
+
+    def setTopicStructure(self,structure):
+        self._set_structure(structure)
 
     def getOwnerSheet(self):
         parent = self.getParentNode()