It is a list of integers, separated by coma, to control whether to span a cell over several columns. The first number in the list denotes the number of columns the first cell shall span. The second number denotes that of the second cell and so on. If the number is omitted, 1 is assumed.

For example,

<grid>
    <columns>    
        <column label="Left" align="left"/><column label="Center" align="center"/>        
        <column label="Right" align="right"/><column label="Column 4"/>        
        <column label="Column 5"/><column label="Column 6"/>        
    </columns>    
    <rows>    
        <row>        
            <label value="Item A.1"/><label value="Item A.2"/>            
            <label value="Item A.3"/><label value="Item A.4"/>            
            <label value="Item A.5"/><label value="Item A.6"/>            
        </row>        
        <row spans="1,2,2">        
            <label value="Item B.1"/><label value="Item B.2"/>            
            <label value="Item B.4"/><label value="Item B.6"/>            
        </row>        
        <row spans="3">        
            <label value="Item C.1"/><label value="Item C.4"/>            
            <label value="Item C.5"/><label value="Item C.6"/>            
        </row>        
        <row spans=",,2,2">        
            <label value="Item D.1"/><label value="Item D.2"/>            
            <label value="Item D.3"/><label value="Item D.5"/>            
        </row>        
    </rows>    
</grid>