code: function() {
          var propertyStyles = {};
  
          // check the default style
          var style = this.defaultStyle;
          this.addPropertyStyles(propertyStyles, style);
  
          // walk through all rules to check for properties in their symbolizer
          var rules = this.rules;
          var symbolizer, value;
          for (var i=0, len=rules.length; i<len; i++) {
              symbolizer = rules[i].symbolizer;
              for (var key in symbolizer) {
                  value = symbolizer[key];
                  if (typeof value == "object") {
                      // symbolizer key is "Point", "Line" or "Polygon"
                      this.addPropertyStyles(propertyStyles, value);
                  } else {
                      // symbolizer is a hash of style properties
                      this.addPropertyStyles(propertyStyles, symbolizer);
                      break;
                  }
              }
          }
          return propertyStyles;
      }
docs: Method: findPropertyStyles
  Looks into all rules for this style and the defaultStyle to collect
  all the style hash property names containing ${...} strings that have
  to be replaced using the createLiteral method before returning them.
  
  Returns:
  {Object} hash of property names that need createLiteral parsing. The
  name of the property is the key, and the value is true;