Document geometry argument of the feature callback for internal use

src/ol/renderer/vector.js

@@ -7,6 +7,11 @@ import ImageState from '../ImageState.js';
 import {getUid} from '../util.js';
 
 /**
+ * Feature callback. The callback will be called with three arguments. The first
+ * argument is one {@link module:ol/Feature feature} or {@link module:ol/render/Feature render feature}
+ * at the pixel, the second is the {@link module:ol/layer/Layer layer} of the feature and will be null for
+ * unmanaged layers. The third is the {@link module:ol/geom/SimpleGeometry} of the feature. For features
+ * with a GeometryCollection geometry, it will be the first detected geometry from the collection.
  * @template T
  * @typedef {function(import("../Feature.js").FeatureLike, import("../layer/Layer.js").default, import("../geom/SimpleGeometry.js").default): T} FeatureCallback
  */