mapnik/tests/visual_tests/styles/text-halo-opacity.xml

<Map 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" background-color="steelblue" minimum-version="3.0.0">
    <Parameters>
        <Parameter name="sizes">512,512</Parameter>
    </Parameters>

    <Style name="labels">
        <Rule>
            <Filter>([id]=1)</Filter>
            <TextSymbolizer
              face-name="DejaVu Sans Book"
              size="15"
              halo-radius="4"
              halo-opacity="1.0"
              >
              'halo-opacity = 1.0'
            </TextSymbolizer>
        </Rule>
        <Rule>
            <Filter>([id]=2)</Filter>
            <TextSymbolizer
              face-name="DejaVu Sans Book"
              size="15"
              halo-radius="4"
              halo-opacity="0.75"
              >
              'halo-opacity = 0.75'
            </TextSymbolizer>
        </Rule>
        <Rule>
            <Filter>([id]=3)</Filter>
            <TextSymbolizer
              face-name="DejaVu Sans Book"
              size="15"
              halo-radius="4"
              halo-opacity="0.5"
            >
              'halo-opacity = 0.5'
            </TextSymbolizer>
        </Rule>
        <Rule>
            <Filter>([id]=4)</Filter>
            <TextSymbolizer
              face-name="DejaVu Sans Book"
              size="15"
              halo-radius="4"
              halo-opacity="0.25"
            >
                'halo-opacity = 0.25'
            </TextSymbolizer>
        </Rule>
    </Style>

    <Layer name="point" srs="+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs">
        <StyleName>labels</StyleName>
        <Datasource>
            <Parameter name="type">csv</Parameter>
            <Parameter name="inline">
id,x,y
1,1.5,4.5
2,1.5,3.5
3,1.5,2.5
4,1.5,1.5
            </Parameter>
        </Datasource>
    </Layer>

    <!-- points to frame data view -->

    <Style name="frame">
        <Rule>
            <PointSymbolizer />
        </Rule>
    </Style>

    <Layer name="frame" srs="+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs">
        <StyleName>frame</StyleName>
        <Datasource>
            <Parameter name="type">csv</Parameter>
            <Parameter name="inline">
x,y
0,0
5,0
0,5
5,5
            </Parameter>
        </Datasource>
    </Layer>
</Map>