diff --git a/externs/olx.js b/externs/olx.js
index 949efbb640..89a00b2617 100644
--- a/externs/olx.js
+++ b/externs/olx.js
@@ -5,88 +5,6 @@
 let olx;
 
 
-/**
- * Object literal with config options for the projection.
- * @typedef {{code: string,
- *     units: (ol.proj.Units|string|undefined),
- *     extent: (ol.Extent|undefined),
- *     axisOrientation: (string|undefined),
- *     global: (boolean|undefined),
- *     metersPerUnit: (number|undefined),
- *     worldExtent: (ol.Extent|undefined),
- *     getPointResolution: (function(number, ol.Coordinate):number|undefined) }}
- */
-olx.ProjectionOptions;
-
-
-/**
- * The SRS identifier code, e.g. `EPSG:4326`.
- * @type {string}
- * @api
- */
-olx.ProjectionOptions.prototype.code;
-
-
-/**
- * Units. Required unless a proj4 projection is defined for `code`.
- * @type {ol.proj.Units|string|undefined}
- * @api
- */
-olx.ProjectionOptions.prototype.units;
-
-
-/**
- * The validity extent for the SRS.
- * @type {ol.Extent|undefined}
- * @api
- */
-olx.ProjectionOptions.prototype.extent;
-
-
-/**
- * The axis orientation as specified in Proj4. The default is `enu`.
- * @type {string|undefined}
- * @api
- */
-olx.ProjectionOptions.prototype.axisOrientation;
-
-
-/**
- * Whether the projection is valid for the whole globe. Default is `false`.
- * @type {boolean|undefined}
- * @api
- */
-olx.ProjectionOptions.prototype.global;
-
-
-/**
- * The meters per unit for the SRS. If not provided, the `units` are used to get
- * the meters per unit from the {@link ol.proj.METERS_PER_UNIT} lookup table.
- * @type {number|undefined}
- * @api
- */
-olx.ProjectionOptions.prototype.metersPerUnit;
-
-
-/**
- * The world extent for the SRS.
- * @type {ol.Extent|undefined}
- * @api
- */
-olx.ProjectionOptions.prototype.worldExtent;
-
-
-/**
- * Function to determine resolution at a point. The function is called with a
- * `{number}` view resolution and an `{ol.Coordinate}` as arguments, and returns
- * the `{number}` resolution at the passed coordinate. If this is `undefined`,
- * the default {@link ol.proj#getPointResolution} function will be used.
- * @type {(function(number, ol.Coordinate):number|undefined)}
- * @api
- */
-olx.ProjectionOptions.prototype.getPointResolution;
-
-
 /**
  * @typedef {{
  *   center: (ol.Coordinate|undefined),
diff --git a/externs/xol.js b/externs/xol.js
index 129fafce20..bc2ece3e65 100644
--- a/externs/xol.js
+++ b/externs/xol.js
@@ -1,21 +1,4 @@
 
-/**
- * @typedef {Object} ProjectionOptions
- * @property {string} code The SRS identifier code, e.g. `EPSG:4326`.
- * @property {ol.proj.Units|string|undefined} units Units. Required unless a proj4 projection is defined for `code`.
- * @property {ol.Extent|undefined} extent The validity extent for the SRS.
- * @property {string|undefined} axisOrientation The axis orientation as specified in Proj4. The default is `enu`.
- * @property {boolean|undefined} global Whether the projection is valid for the whole globe. Default is `false`.
- * @property {number|undefined} metersPerUnit The meters per unit for the SRS. If not provided, the `units` are used to get
- * the meters per unit from the {@link ol.proj.METERS_PER_UNIT} lookup table.
- * @property {ol.Extent|undefined} worldExtent The world extent for the SRS.
- * @property {(function(number, ol.Coordinate):number|undefined)} getPointResolution Function to determine resolution at a point. The function is called with a
- * `{number}` view resolution and an `{ol.Coordinate}` as arguments, and returns
- * the `{number}` resolution at the passed coordinate. If this is `undefined`,
- * the default {@link ol.proj#getPointResolution} function will be used.
- */
-
-
 /**
  * @typedef {Object} AnimationOptions
  * @property {ol.Coordinate|undefined} center The center of the view at the end of the animation.
diff --git a/src/ol/proj/Projection.js b/src/ol/proj/Projection.js
index eb572f0ebc..5829dbb780 100644
--- a/src/ol/proj/Projection.js
+++ b/src/ol/proj/Projection.js
@@ -3,6 +3,29 @@
  */
 import {METERS_PER_UNIT} from '../proj/Units.js';
 
+
+/**
+ * @typedef {Object} Options
+ * @property {string} code The SRS identifier code, e.g. `EPSG:4326`.
+ * @property {ol.proj.Units|string|undefined} units Units. Required unless a
+ * proj4 projection is defined for `code`.
+ * @property {ol.Extent|undefined} extent The validity extent for the SRS.
+ * @property {string|undefined} axisOrientation The axis orientation as specified
+ * in Proj4. The default is `enu`.
+ * @property {boolean|undefined} global Whether the projection is valid for the
+ * whole globe. Default is `false`.
+ * @property {number|undefined} metersPerUnit The meters per unit for the SRS.
+ * If not provided, the `units` are used to get the meters per unit from the {@link ol.proj.METERS_PER_UNIT}
+ * lookup table.
+ * @property {ol.Extent|undefined} worldExtent The world extent for the SRS.
+ * @property {(function(number, ol.Coordinate):number|undefined)} getPointResolution
+ * Function to determine resolution at a point. The function is called with a
+ * `{number}` view resolution and an `{ol.Coordinate}` as arguments, and returns
+ * the `{number}` resolution at the passed coordinate. If this is `undefined`,
+ * the default {@link ol.proj#getPointResolution} function will be used.
+ */
+
+
 /**
  * @classdesc
  * Projection definition class. One of these is created for each projection
@@ -29,7 +52,7 @@ import {METERS_PER_UNIT} from '../proj/Units.js';
  * namespace for proj4, use {@link ol.proj.setProj4}.
  *
  * @constructor
- * @param {olx.ProjectionOptions} options Projection options.
+ * @param {module:ol/proj/Projection~Options} options Projection options.
  * @struct
  * @api
  */