Are all nexted elements implemented as DataType extensions?

[McCollum , Angus]

I created a custom Ant task with a nested element. I had writen the nested
element as a Task but failed to get the addXXXX method called on the
enclosing task.

I took a look at the Ant source and noticed that all the examples I found
used nested element that were DataTypes and not Tasks. Is this always the
case? Should I have structed my nested element as a DataType and not a Task?

Thank you in advance.

G. Angus McCollum