extra_arbitary_map_parameters.xml

<Map>

<!-- 
     totally arbirary Parameters can also be attached to the map
     which will be respected during serialization.
     
     This makes it easier for calling applications that work with mapnik
     xml, and leverage its serialization, to pass through directives that
     the calling application needs which describe how to handle the map.
-->

  <Parameters>
    <Parameter name="key" type="string"><![CDATA[value]]></Parameter>
    <!-- this one will override previous key with same name -->
    <Parameter name="key" type="string"><![CDATA[value2]]></Parameter>
    <Parameter name="key3" type="string"><![CDATA[value3]]></Parameter>
    <Parameter name="unicode" type="string"><![CDATA[iván]]></Parameter>
    <Parameter name="integer" type="int"><![CDATA[10]]></Parameter>
    <Parameter name="decimal" type="float"><![CDATA[.999]]></Parameter>
    <!-- without a type attribute numbers are treated as strings -->
    <Parameter name="number-as-string"><![CDATA[.9998]]></Parameter>
  </Parameters>

</Map>