gistfile1.pl

    $form->populate( {
        auto_fieldset   => { id => 'fs_login_form' },
        elements        => [
{ type => 'Block', tag => 'dl', elements => [

{ type => 'Block', content => 'Username', tag => 'dt' },
 { type => 'Block', tag => 'dd', elements =>
            {   type        => 'Text',
                name        => 'login_login',
                constraints => [qw|Required|],

            },

                attrs => { class => 'data' },
 }
        ] } ],
    } );

# gives me

<form action="" method="post">
<fieldset id="fs_login_form">
<dl>
<dt>
Username
</dt>
<dd class="data">
<div class="text">
<input name="login_login" type="text" />
</div>
</dd>
</dl>