I know it doesn't have any buttons, but this is what I have tried:
xml code:
<Window Id="WndSearch" Version="1">
    <Position Width="400" Height="150"/>
    <ChildTmpl>
    <Controls>
        <Control xsi:type="StaticControl" Id="InfoTxt">
            <Position Left="8" Top="3" Width="370"/>
            <Caption>Enter the text to search for, and click Search to open a results window.</Caption>
        </Control>
        <Control xsi:type="EditControl" Id="EdtSearch">
            <Position Left="8" Top="23" Width="370"/>
            <Help>Enter a search query...</Help>
        </Control>
    </Controls>
</Window>
I have also tried using the exact window mentioned above:
xml code:
<Window Id="WndChildExample" Version="1">
   <ChildTmpl/>
   <Position Width="243" Height="193"/>
   <Controls>
      <Control xsi:type="StaticControl" Id="lblTitle">
         <Position Top="25" Width="100" Left="15" Height="15" />
         <Caption>hi I am a child window :)</Caption>
      </Control>
   </Controls>
</Window>