Nested Beans

<a> <afield1> content1 </afield1> <b> 
<bfield1> content2 </bfield1> </b><b> <bfield2> content3 </bfield2> </b> </a>
 
<a> <afield1> content4 </afield1> <b> 
<bfield1> content5 </bfield1> </b><b> <bfield2> content5 </bfield2> </b> </a>
 
....

If I want to keep the structure in my JasperReport, It looks like I need to place a 'detail' section within a 'detail' section. I was told I have to use 'Nested Beans' and 'table or cross tabs' to achieve this, but I cannot find any information of use in the web. Can somebody enlighten me?