docs: function(feature) {
          if (!feature) return null;
  
          var featureName = feature.eClass ? feature.get('name') : feature;
  
          if (!_.has(this.values, featureName) && this.has(featureName)) {
              initValue(this, getEStructuralFeature(this.eClass, featureName));
          }
  
          var value = this.values[featureName];
  
          if (typeof value === 'function') {
              return value.apply(this);
          } else {
              return value;
          }
      }