Fieldset is used for logical grouping of controls using border with a legend
See the TLD docs @ http://myfaces.apache.org/tomahawk/tlddoc/t/fieldset.html
W3C recommentation @ http://www.w3.org/TR/REC-html40/interact/forms.html#edef-FIELDSET
Example
<t:fieldset legend="private address">
<h:panelGrid columns="2">
<h:outputText value=" " />
<t:selectOneRadio id="carChoice" value="#{theTestBean.carChoice}" layout="spread" >
<f:selectItem itemValue="0" itemLabel="Mr." />
<f:selectItem itemValue="1" itemLabel="Mrs." />
</t:selectOneRadio>
<h:outputText value="Name:" />
<h:inputText id="name" />
<h:outputText value="Last Name:" />
<h:inputText id="lastname" />
</h:panelGrid>
<t:fieldset />