mapnik/tests/data/good_maps/style_level_opacity_and_blur.xml

<Map background-color="#fcc" srs="+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0.0 +k=1.0 +units=m +nadgrids=@null +wktext +no_defs +over">
    <!-- Asia -->
    <Style name="style" image-filters="agg-stack-blur(4,4)">
        <Rule>
            <Filter>([REGION]=142)</Filter>
            <PolygonSymbolizer fill="yellow"/>
        </Rule>
    </Style>
    <!-- Not Asia -->
    <Style name="style2" opacity=".5">
        <Rule>
            <Filter>([REGION]!=142)</Filter>
            <PolygonSymbolizer fill="#fff"/>
        </Rule>
    </Style>
    <Layer name="world" srs="+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0.0 +k=1.0 +units=m +nadgrids=@null +wktext +no_defs +over">
        <StyleName>style</StyleName>
        <StyleName>style2</StyleName>
        <Datasource>
            <Parameter name="file">../shp/world_merc</Parameter>
            <Parameter name="type">shape</Parameter>
        </Datasource>
    </Layer>
</Map>