In addition to columns, you can specify auxiliary headers with the auxhead and auxheader components as follows.

<grid>
    <auxhead>    
        <auxheader label="H1'07" colspan="6"/>        
        <auxheader label="H2'07" colspan="6"/>        
    </auxhead>    
    <auxhead>    
        <auxheader label="Q1" colspan="3"/>        
        <auxheader label="Q2" colspan="3"/>        
        <auxheader label="Q3" colspan="3"/>        
        <auxheader label="Q4" colspan="3"/>        
    </auxhead>    
    <columns>    
        <column label="Jan"/><column label="Feb"/><column label="Mar"/>        
        <column label="Apr"/><column label="May"/><column label="Jun"/>        
        <column label="Jul"/><column label="Aug"/><column label="Sep"/>        
        <column label="Oct"/><column label="Nov"/><column label="Dec"/>        
    </columns>    
    <rows>    
        <row>        
        <label value="1,000"/><label value="1,100"/><label value="1,200"/>        
        <label value="1,300"/><label value="1,400"/><label value="1,500"/>        
        <label value="1,600"/><label value="1,700"/><label value="1,800"/>        
        <label value="1,900"/><label value="2,000"/><label value="2,100"/>        
        </row>        
    </rows>    
</grid>

The auxiliary headers support the colspan and rowsspan properties that the column header don't. However, as its name suggested, the auxiliary headers must be used with column.

Unlike column/columns, which can used only with grid, auhead/auxheader can be used with grid, listbox and tree.