code: function(propertyStyles, symbolizer) {
          var property;
          for (var key in symbolizer) {
              property = symbolizer[key];
              if (typeof property == "string" &&
                      property.match(/\$\{\w+\}/)) {
                  propertyStyles[key] = true;
              }
          }
          return propertyStyles;
      }
docs: Method: addPropertyStyles
  
  Parameters:
  propertyStyles - {Object} hash to add new property styles to. Will be
  modified inline
  symbolizer     - {Object} search this symbolizer for property styles
  
  Returns:
  {Object} propertyStyles hash