docs: function(attrName, attrValue) {
          var i,
              feature,    
              len = this.features.length,
              foundFeatures = [];
          for(i = 0; i < len; i++) {            
              feature = this.features[i];
              if(feature && feature.attributes) {
                  if (feature.attributes[attrName] === attrValue) {
                      foundFeatures.push(feature);
                  }
              }
          }
          return foundFeatures;
      }