mapnik/tests/data/good_maps/style_level_comp_op.xml

<Map srs="+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs"
     background-color="lightsteelblue">

  <Style name="land">
    <Rule>
      <PolygonSymbolizer fill="darkslategrey" geometry-transform="translate(+1,+1)" />
      <PolygonSymbolizer fill="lightcyan"     geometry-transform="translate(-1,-1)" />
      <PolygonSymbolizer fill="forestgreen" />
    </Rule>
  </Style>

  <Style name="markers" comp-op="src-over">
    <Rule>
      <MarkersSymbolizer fill="saddlebrown"
                         fill-opacity="0.5"
                         stroke-width="0"
                         width="45 - 5 * [SCALERANK]"
                         height="45 - 5 * [SCALERANK]"
                         allow-overlap="true"
                         ignore-placement="true"
                         />
      <MarkersSymbolizer fill="white"
                         fill-opacity="0.7"
                         stroke-width="0"
                         width="5"
                         height="5"
                         allow-overlap="true"
                         ignore-placement="true"
                         />
    </Rule>
  </Style>

  <Layer name="land">
    <StyleName>land</StyleName>
    <Datasource>
      <Parameter name="type">shape</Parameter>
      <Parameter name="file">../shp/new_zealand/ne_50m_land.shp</Parameter>
    </Datasource>
  </Layer>

  <Layer name="cities">
    <StyleName>markers</StyleName>
    <Datasource>
      <Parameter name="type">shape</Parameter>
      <Parameter name="file">../shp/new_zealand/ne_50m_populated_places_simple.shp</Parameter>
    </Datasource>
  </Layer>

</Map>