(Quick Reference)
                ui:fieldGroup
Purpose
A grouping container for a set of form elements. Typically equivalent to a <fieldset> but a UI Set may add extra structural markup.
Example
<ui:form controller="book"> 
  <ui:fieldGroup>
     <ui:field name="firstName"/>
     <ui:field name="lastName"/>
  </ui:fieldGroup>
  <ui:fieldGroup>
     <ui:field name="email"/>
  </ui:fieldGroup>
  <ui:actions>
    <ui:button type="submit">Save</ui:button>
  </ui:actions>
</ui:form>
Attributes
None. The body is used as the label content for the outer 
field tag.