Tiles Definition: Nested

The following is an example of nested Tiles Definition:

<definition name="myapp.homepage.body" template="/layouts/three_rows.jsp">
  <put-attribute name="one" value="/tiles/headlines.jsp" />
  <put-attribute name="two" value="/tiles/topics.jsp" />
  <put-attribute name="one" value="/tiles/comments.jsp" />
</definition>

<definition name="myapp.homepage" template="/layouts/classic.jsp">
  <put-attribute name="title" value="Tiles tutorial homepage" />
  <put-attribute name="header" value="/tiles/banner.jsp" />
  <put-attribute name="menu" value="/tiles/common_menu.jsp" />
  <put-attribute name="body" value="myapp.homepage.body" />
  <put-attribute name="footer" value="/tiles/credits.jsp" />
</definition>

The following apache link provides some very good information on Tiles Definition.
http://tiles.apache.org/framework/tutorial/advanced/nesting-extending.html