diff --git a/docs/getting-started/v3-migration.md b/docs/getting-started/v3-migration.md
index 9791b5025ba..47d0c741fac 100644
--- a/docs/getting-started/v3-migration.md
+++ b/docs/getting-started/v3-migration.md
@@ -63,6 +63,8 @@ Chart.js 3.0 introduces a number of breaking changes. Chart.js 2.0 was released
 * `scales.[x/y]Axes.time.max` was renamed to `scales[id].max`
 * `scales.[x/y]Axes.time.min` was renamed to `scales[id].min`
 * The dataset option `tension` was renamed to `lineTension`
+* To override the platform class used in a chart instance, pass `platform: PlatformClass` in the config object. Note that the class should be passed, not an instance of the class.
+* To disable CSS injection (necessary in some iframe contexts), `Chart.platform.disableCSSInjection = true` is no longer supported. Pass `disableCSSInjection: true` in the config object instead.
 
 ### Animations
 
@@ -161,6 +163,7 @@ Animation system was completely rewritten in Chart.js v3. Each property can now
 
 * `helpers._alignPixel` was renamed to `helpers.canvas._alignPixel`
 * `helpers._decimalPlaces` was renamed to `helpers.math._decimalPlaces`
+* `chart.initialize` was renamed to `chart._initialize` (labeled as private but not named as such)
 
 ### Changed
 
@@ -211,5 +214,3 @@ Animation system was completely rewritten in Chart.js v3. Each property can now
 * `Chart.platform` no longer exists. Every chart instance now has a separate platform instance, `chart.platform`.
 * `Chart.platforms` is an object that contains two usable platform classes, `BasicPlatform` and `DomPlatform`. It also contains `Platform`, a class that all platforms must extend from.
 * If the canvas passed in is an instance of `OffscreenCanvas`, the `BasicPlatform` is automatically used.
-* T override the platform class used in a chart instance, pass `platform: PlatformClass` in the config object. Note that the class should be passed, not an instance of the class.
-* To disable CSS injection (necessary in some iframe contexts), `Chart.platform.disableCSSInjection = true` is no longer supported. Pass `disableCSSInjection: true` in the config object instead.
diff --git a/src/core/core.controller.js b/src/core/core.controller.js
index 9adbc03356c..6a274bd6899 100644
--- a/src/core/core.controller.js
+++ b/src/core/core.controller.js
@@ -152,7 +152,7 @@ function onAnimationProgress(ctx) {
  * Chart.js can take a string id of a canvas element, a 2d context, or a canvas element itself.
  * Attempt to unwrap the item passed into the chart constructor so that it is a canvas element (if possible).
  */
-function unwrapItem(item) {
+function getCanvas(item) {
 	if (typeof document !== undefined && typeof item === 'string') {
 		item = document.getElementById(item);
 	} else if (item.length) {
@@ -172,10 +172,10 @@ class Chart {
 		const me = this;
 
 		config = initConfig(config);
-		const unwrappedItem = unwrapItem(item);
-		me.initializePlatform(unwrappedItem, config);
+		const initialCanvas = getCanvas(item);
+		me._initializePlatform(initialCanvas, config);
 
-		const context = me.platform.acquireContext(unwrappedItem, config);
+		const context = me.platform.acquireContext(initialCanvas, config);
 		const canvas = context && context.canvas;
 		const height = canvas && canvas.height;
 		const width = canvas && canvas.width;
@@ -217,14 +217,14 @@ class Chart {
 		Animator.listen(me, 'complete', onAnimationsComplete);
 		Animator.listen(me, 'progress', onAnimationProgress);
 
-		me.initialize();
+		me._initialize();
 		me.update();
 	}
 
 	/**
 	 * @private
 	 */
-	initialize() {
+	_initialize() {
 		const me = this;
 
 		// Before init plugin notification
@@ -250,17 +250,14 @@ class Chart {
 	/**
 	 * @private
 	 */
-	initializePlatform(item, config) {
+	_initializePlatform(canvas, config) {
 		const me = this;
 
 		if (config.platform) {
-			if (!(config.platform instanceof Platform)) {
-				throw new Error('If config.platform is used, it must be an instance of Chart.platforms.Platform or one of its descendants');
-			}
 			me.platform = new config.platform(config);
-		} else if (typeof window === 'undefined' || typeof document === 'undefined' || !item) {
+		} else if (typeof window === 'undefined' || typeof document === 'undefined') {
 			me.platform = new BasicPlatform(config);
-		} else if (window.OffscreenCanvas && item instanceof window.OffscreenCanvas) {
+		} else if (window.OffscreenCanvas && canvas instanceof window.OffscreenCanvas) {
 			me.platform = new BasicPlatform(config);
 		} else {
 			me.platform = new DomPlatform(config);
diff --git a/src/platforms/platform.dom.js b/src/platforms/platform.dom.js
index d3a08478338..e11a4d4fdf1 100644
--- a/src/platforms/platform.dom.js
+++ b/src/platforms/platform.dom.js
@@ -315,10 +315,13 @@ function injectCSS(rootNode, css) {
 
 /**
  * Platform class for charts that can access the DOM and global window/document properties
- * @constructor
  * @extends Platform
  */
 export default class DomPlatform extends Platform {
+	/**
+	 * @constructor
+	 * @param {object} options - The chart options
+	 */
 	constructor(options) {
 		super();
 
@@ -329,7 +332,7 @@ export default class DomPlatform extends Platform {
 		 * to be manually imported to make this library compatible with any CSP.
 		 * See https://github.com/chartjs/Chart.js/issues/5208
 		 */
-		this.disableCSSInjection = options.disableCSSInjection || false;
+		this.disableCSSInjection = options.disableCSSInjection;
 	}
 
 	/**
@@ -348,24 +351,24 @@ export default class DomPlatform extends Platform {
 		}
 	}
 
-	acquireContext(item, config) {
+	acquireContext(canvas, config) {
 		// To prevent canvas fingerprinting, some add-ons undefine the getContext
 		// method, for example: https://github.com/kkapsner/CanvasBlocker
 		// https://github.com/chartjs/Chart.js/issues/2807
-		var context = item && item.getContext && item.getContext('2d');
+		var context = canvas && canvas.getContext && canvas.getContext('2d');
 
-		// `instanceof HTMLCanvasElement/CanvasRenderingContext2D` fails when the item is
+		// `instanceof HTMLCanvasElement/CanvasRenderingContext2D` fails when the canvas is
 		// inside an iframe or when running in a protected environment. We could guess the
 		// types from their toString() value but let's keep things flexible and assume it's
-		// a sufficient condition if the item has a context2D which has item as `canvas`.
+		// a sufficient condition if the canvas has a context2D which has canvas as `canvas`.
 		// https://github.com/chartjs/Chart.js/issues/3887
 		// https://github.com/chartjs/Chart.js/issues/4102
 		// https://github.com/chartjs/Chart.js/issues/4152
-		if (context && context.canvas === item) {
+		if (context && context.canvas === canvas) {
 			// Load platform resources on first chart creation, to make it possible to
 			// import the library before setting platform options.
-			this._ensureLoaded(item);
-			initCanvas(item, config);
+			this._ensureLoaded(canvas);
+			initCanvas(canvas, config);
 			return context;
 		}
 
diff --git a/src/platforms/platform.js b/src/platforms/platform.js
index d7765334b8f..2200221c93a 100644
--- a/src/platforms/platform.js
+++ b/src/platforms/platform.js
@@ -5,14 +5,16 @@
  */
 export default class Platform {
 	/**
-	 * @param {object} options - The chart options
+	 * @constructor
+	 * The Platform constructor has no required parameters, but chart options are passed in as
+	 * the first and only parameter to all Platform constructors.
 	 */
 	constructor() {}
 
 	/**
 	 * Called at chart construction time, returns a context2d instance implementing
 	 * the [W3C Canvas 2D Context API standard]{@link https://www.w3.org/TR/2dcontext/}.
-	 * @param {*} item - The native item from which to acquire context (platform specific)
+	 * @param {canvas} canvas - The canvas from which to acquire context (platform specific)
 	 * @param {object} options - The chart options
 	 * @returns {CanvasRenderingContext2D} context2d instance
 	 */