The last two Columns should shrink to 0 width.

<listbox width="400px">
<listhead>
<listheader label="Product" width="250px" />
<listheader label="Description" width="250px" />
<listheader label="Comment" hflex="2" />
<listheader label="Comment 2" hflex="1" />
</listhead>
<listitem forEach="1,2,3">
<listcell forEach="1,2,3,4">Listcell</listcell>
</listitem>
</listbox>