mapnik/tests/visual_tests/styles/shield-on-line-spacing-eq-width.xml

<Map background-color="steelblue" srs="+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs">
    <Layer name="layer" srs="+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs">
        <StyleName>alpha</StyleName>
        <Datasource>
            <Parameter name="type">csv</Parameter>
            <Parameter name="inline">
            wkt,halo-opacity,text-opacity,opacity
            "LINESTRING(0 0, 10 2)",.1,.1,.1
            </Parameter>
        </Datasource>
    </Layer>
    <Layer name="layer" srs="+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs">
        <StyleName>beta</StyleName>
        <Datasource>
            <Parameter name="type">csv</Parameter>
            <Parameter name="inline">
            wkt,halo-opacity,text-opacity,opacity
            "LINESTRING(0 2, 10 4)",1,1,1
            </Parameter>
        </Datasource>
    </Layer>
    <Layer name="layer" srs="+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs">
        <StyleName>gamma</StyleName>
        <Datasource>
            <Parameter name="type">csv</Parameter>
            <Parameter name="inline">
            wkt,halo-opacity,text-opacity,opacity
            "LINESTRING(0 4, 10 6)",1,1,1
            </Parameter>
        </Datasource>
    </Layer>

    <Style name="alpha">
        <Rule>
            <ShieldSymbolizer
              file="../../data/svg/rect.svg"
              placement="point"
              face-name="DejaVu Sans Book"
              halo-fill="white"
              halo-radius="2"
              spacing="1"
              halo-opacity="[halo-opacity]"
              text-opacity="[text-opacity]"
              opacity="[opacity]"
              minimum-distance="20">
            'hi'
            </ShieldSymbolizer>
            <TextSymbolizer
              placement="line"
              face-name="DejaVu Sans Book"
              halo-fill="black"
              fill="white"
              size="20"
              halo-radius="2"
              halo-rasterizer="fast"
              halo-opacity="[halo-opacity]"
              opacity="[opacity]"
              spacing="15">
            'there'
            </TextSymbolizer>
            <LineSymbolizer stroke-width="0.2" stroke="#ff0000" />
        </Rule>
    </Style>
    <Style name="beta">
        <Rule>
            <ShieldSymbolizer
              file="../../data/svg/rect.svg"
              placement="line"
              face-name="DejaVu Sans Book"
              halo-fill="white"
              halo-radius="2"
              halo-opacity="[halo-opacity]"
              text-opacity="[text-opacity]"
              opacity="[opacity]"
              spacing="20">
            'hi'
            </ShieldSymbolizer>
            <LineSymbolizer stroke-width="0.2" stroke="#ff0000" />
        </Rule>
    </Style>
    <Style name="gamma">
        <Rule>
            <ShieldSymbolizer
              file="../../data/svg/rect.svg"
              placement="line"
              face-name="DejaVu Sans Book"
              halo-fill="white"
              halo-radius="2"
              halo-rasterizer="fast"
              halo-opacity="[halo-opacity]"
              text-opacity="[text-opacity]"
              opacity="[opacity]"
              spacing="15">
            'hi'
            </ShieldSymbolizer>
            <LineSymbolizer stroke-width="0.2" stroke="#ff0000" />
        </Rule>
    </Style>
</Map>