title: Custom tags in UiBinder files
body: <p>When using a <code>&lt;g:LayoutPanel&gt;</code> in UiBinder.ui.xml files, you can specify <code>&lt;g:layer&gt;</code> tags.  Some other Google-built widgets have special tags like that as well - <code>&lt;g:tab&gt;</code> even has a sub-tag, <code>&lt;g:header&gt;</code>.</p>
  
  <p>How can I specify these for my own widgets?</p>