append Zend Form display group name into element's name

I want to append group's name into element's name the same way sub form appends its name. If I add a subform named 'basicDetails' and add a text field 'firstName' into the sub form the code will be something

<input type="text" value="" id="basicDetails-firstName" name="basicDetails[firstName]" />

Code (markup):

I want to achieve the same with groups so if I add a group 'personalInformation' in the subform and add the 'firstName' element into this group, ZF generate

<input type="text" value="" id="basicDetails-personalInformation-firstName" name="basicDetails[personalInformation][firstName]" />

Code (markup):

any suggestions

 

Why not generate another subform instead of a group, since they both use fieldset decorator and Zend supports nested subforms?

$form = new Zend_Form();
$form->addElement('Text','username');
$sForm = new Zend_Form_SubForm();
$sForm->addElement('Text','email');
$form->addSubForm($sForm, 'basicDetails');

$ssForm = new Zend_Form_SubForm();
$ssForm->addElement('Text','firstName');
$sForm->addSubForm($ssForm, 'personalInformation');

echo $form->render();

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