Incorporate review comments of ahocevar and tschaub.

src/ol/PluggableMap.js

@@ -61,7 +61,7 @@ import {create as createTransform, apply as applyTransform} from './transform.js
 
 /**
  * @typedef {Object} AtPixelOptions
- * @property {function(module:ol/layer/Layer): boolean|undefined} layerFilter Layer filter
+ * @property {undefined|function(module:ol/layer/Layer): boolean} layerFilter Layer filter
  * function. The filter function will receive one argument, the
  * {@link module:ol/layer/Layer layer-candidate} and it should return a boolean value.
  * Only layers which are visible and for which this function returns `true`

src/ol/format/Feature.js

@@ -200,7 +200,7 @@ export default FeatureFormat;
 /**
  * @param {module:ol/geom/Geometry|module:ol/extent~Extent} geometry Geometry.
  * @param {boolean} write Set to true for writing, false for reading.
- * @param {module:ol/format/Feature~WriteOptions|module:ol/format/Feature~ReadOptions=} opt_options
+ * @param {module:ol/format/Feature~WriteOptions=|module:ol/format/Feature~ReadOptions=} opt_options
  *     Options.
  * @return {module:ol/geom/Geometry|module:ol/extent~Extent} Transformed geometry.
  */