diff --git src/wp-includes/js/media/controllers/cropper.js src/wp-includes/js/media/controllers/cropper.js
index bfcaf11c9..be4b7bc53 100644
--- src/wp-includes/js/media/controllers/cropper.js
+++ src/wp-includes/js/media/controllers/cropper.js
@@ -4,7 +4,7 @@ var l10n = wp.media.view.l10n,
 /**
  * wp.media.controller.Cropper
  *
- * A state for cropping an image.
+ * A class for cropping an image when called from the header media customization panel.
  *
  * @memberOf wp.media.controller
  *
@@ -26,16 +26,43 @@ Cropper = wp.media.controller.State.extend(/** @lends wp.media.controller.Croppe
 		doCropArgs: {}
 	},
 
+	/**
+	 * @summary Opens the crop image window.
+	 *
+	 * Shows the crop image window when called from the Add new image button.
+	 *
+	 * @since 4.2.0
+	 *
+	 * @returns {void}
+	 */
 	activate: function() {
 		this.frame.on( 'content:create:crop', this.createCropContent, this );
 		this.frame.on( 'close', this.removeCropper, this );
 		this.set('selection', new Backbone.Collection(this.frame._selection.single));
 	},
 
+	/**
+	 * @summary Changes the state of the toolbar window to browse mode.
+	 *
+	 * @since 4.2.0
+	 *
+	 * @returns {void}
+	 */
 	deactivate: function() {
 		this.frame.toolbar.mode('browse');
 	},
 
+	/**
+	 * @summary Creates the crop image window.
+	 *
+	 * Initialized when clicking on the Select and Crop button.
+	 *
+	 * @since 4.2.0
+	 *
+	 * @fires crop window
+	 *
+	 * @returns {void}
+	 */
 	createCropContent: function() {
 		this.cropperView = new wp.media.view.Cropper({
 			controller: this,
@@ -45,12 +72,28 @@ Cropper = wp.media.controller.State.extend(/** @lends wp.media.controller.Croppe
 		this.frame.content.set(this.cropperView);
 
 	},
+
+	/**
+	 * @summary Removes the image selection and closes the cropping window.
+	 *
+	 * @since 4.2.0
+	 *
+	 * @returns {void}
+	 */
 	removeCropper: function() {
 		this.imgSelect.cancelSelection();
 		this.imgSelect.setOptions({remove: true});
 		this.imgSelect.update();
 		this.cropperView.remove();
 	},
+
+	/**
+	 * @summary Checks if cropping can be skipped and creates crop toolbar accordingly.
+	 *
+	 * @since 4.2.0
+	 *
+	 * @returns {void}
+	 */
 	createCropToolbar: function() {
 		var canSkipCrop, toolbarOptions;
 
@@ -106,6 +149,13 @@ Cropper = wp.media.controller.State.extend(/** @lends wp.media.controller.Croppe
 		this.frame.toolbar.set( new wp.media.view.Toolbar(toolbarOptions) );
 	},
 
+	/**
+	 * @summary Creates an object with the image attachment and crop properties.
+	 *
+	 * @since 4.2.0
+	 *
+	 * @returns {$.promise} A jQuery promise with the custom header crop details.
+	 */
 	doCrop: function( attachment ) {
 		return wp.ajax.post( 'custom-header-crop', _.extend(
 			{},