The column of Portallayout.

Child of Portalchildren can only be Panel.

<portallayout>
    <portalchildren width="30%">    
        <panel height="150px" title="Google Tools">        
            <panelchildren>...</panelchildren>            
        </panel>        
        <panel height="300px" title="LabPixies Clock">        
            <panelchildren>...</panelchildren>            
        </panel>        
    </portalchildren>    
    <portalchildren width="30%">    
        <panel height="150px" title="Google Tools">        
            <panelchildren>...</panelchildren>            
        </panel>        
    </portalchildren>    
</portallayout>