There's one ColStyle section for each displayed column.

The ColStyle section contains one or more CellTemplate sections.

One CellTemplate section is enough for the directory styles that display a single content type, e.g. as in the below example, where directory style containing the "Length" column is used only for articles.

<ColStyle Name="Length" Width="80" Height="0" SortName="Length">

  <CellTemplate>

    <xp:TextBlock VerticalAlignment="Top" Text="{Binding Path=[article.bodyTextH], Converter={StaticResource UnitConverter}, ConverterParameter=in::{0:0.00} in}" />

  </CellTemplate>

</ColStyle>

The use of more CellTemplates is explained in Grid for multi-content display.