Maplike and Setlike objects in Map and Set

files/en-us/web/api/audioparammap/index.md

@@ -7,11 +7,11 @@ browser-compat: api.AudioParamMap
 
 {{APIRef("Web Audio API")}}
 
-The Web Audio API interface **`AudioParamMap`** represents a set of multiple audio parameters, each described as a mapping of a string identifying the parameter to the {{domxref("AudioParam")}} object representing its value.
+The **`AudioParamMap`** interface of the [Web Audio API](/en-US/docs/Web/API/Web_Audio_API) represents an iterable and read-only set of multiple audio parameters.
 
-## Instance properties
+`AudioParamMap` is a read-only [`Map`-like object](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map#map-like_objects), in which each key is the name string for a parameter, and the corresponding value is an {{domxref("AudioParam")}} containing the value of that parameter.
 
-The `AudioParamMap` object is accessed as a {{jsxref("Map")}} in which each parameter is identified by a name string which is mapped to an `AudioParam` containing the value of that parameter. In addition, there are the following properties available:
+## Instance properties
 
 - {{domxref("AudioParamMap.size", "size")}}
   - : ?
@@ -29,6 +29,10 @@ The `AudioParamMap` object is accessed as a {{jsxref("Map")}} in which each para
 - {{domxref("AudioParamMap.values", "values()")}}
   - : ?
 
+## Specifications
+
+{{Specifications}}
+
 ## Browser compatibility
 
 {{Compat}}

files/en-us/web/api/customstateset/index.md

@@ -15,8 +15,9 @@ The **`CustomStateSet`** interface of the [Document Object Model](/en-US/docs/We
 
 An HTML form element, such as a checkbox has different _states_, "checked" and "unchecked". Likewise, developers creating custom elements need to assign possible states to these elements. The `CustomStateList` allows these states to be stored, and accessed from the custom element.
 
-An instance of `CustomStateList` is returned by {{domxref("ElementInternals.states")}}. The `CustomStateList` object is described as _setlike_, and therefore the methods behave in a similar manner to those on a {{jsxref("Set")}}.
+An instance of `CustomStateList` is returned by {{domxref("ElementInternals.states")}}.
 
+**`CustomStateList`** is a [`Set`-like object](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set#set-like_objects) that can hold an ordered set of state values.
 Each value stored in a `CustomStateList` is a `<dashed-ident>`, in the format `--mystate`.
 
 ### Interaction with CSS

files/en-us/web/api/eventcounts/index.md

@@ -7,9 +7,9 @@ browser-compat: api.EventCounts
 
 {{APIRef("Performance API")}}
 
-The **`EventCounts`** interface is a read-only map where the keys are event types and the values are the number of events that have been dispatched for that event type.
+The **`EventCounts`** interface of the [Performance API](/en-US/docs/Web/API/Performance_API) provides the number of events that have been dispatched for each event type.
 
-As a read-only map, `EventCounts` is similar to a {{jsxref("Map")}}, however, it doesn't implement the `clear()`, `delete()`, and `set()` methods.
+`EventCounts` is a read-only [`Map`-like object](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map#map-like_objects), in which each key is the name string for an event type, and the corresponding value is an integer indicating the number of events that have been dispatched for that event type.
 
 ## Constructor
 

files/en-us/web/api/fontfaceset/index.md

@@ -9,6 +9,8 @@ browser-compat: api.FontFaceSet
 
 The **`FontFaceSet`** interface of the [CSS Font Loading API](/en-US/docs/Web/API/CSS_Font_Loading_API) manages the loading of font-faces and querying of their download status.
 
+A **`FontFaceSet`** is a [`Set`-like object](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set#set-like_objects) that can hold an ordered set of {{domxref("FontFace")}} objects.
+
 This property is available as {{domxref("Document.fonts")}}, or `self.fonts` in [web workers](/en-US/docs/Web/API/Web_Workers_API).
 
 {{InheritanceDiagram}}

files/en-us/web/api/gpusupportedfeatures/index.md

@@ -9,7 +9,7 @@ browser-compat: api.GPUSupportedFeatures
 
 {{APIRef("WebGPU API")}}{{SeeCompatTable}}
 
-The **`GPUSupportedFeatures`** interface of the {{domxref("WebGPU API", "WebGPU API", "", "nocode")}} is a [setlike](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set) object that describes additional functionality supported by a {{domxref("GPUAdapter")}}.
+The **`GPUSupportedFeatures`** interface of the {{domxref("WebGPU API", "WebGPU API", "", "nocode")}} is a [`Set`-like object](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set#set-like_objects) that describes additional functionality supported by a {{domxref("GPUAdapter")}}.
 
 The `GPUSupportedFeatures` object for the current adapter is accessed via the {{domxref("GPUAdapter.features")}} property.
 
@@ -28,14 +28,14 @@ We have not listed the exact set of additional features available to be used in
 
 ## Instance properties
 
-The following properties are available to all read-only [setlike](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set) objects (the below links are to the {{jsxref("Set")}} global object reference pages).
+The following properties are available to all read-only [`Set`-like](/en-US/docs/Glossary/Setlike_object) objects (the below links are to the {{jsxref("Set")}} global object reference pages).
 
 - {{jsxref("Set.prototype.size", "size")}} {{Experimental_Inline}}
   - : Returns the number of values in the set.
 
 ## Instance methods
 
-The following methods are available to all read-only [setlike](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set) objects (the below links are to the {{jsxref("Set")}} global object reference pages).
+The following methods are available to all read-only [`Set`-like](/en-US/docs/Glossary/Setlike_object) objects (the below links are to the {{jsxref("Set")}} global object reference pages).
 
 - {{jsxref("Set.prototype.has()", "has()")}} {{Experimental_Inline}}
   - : Returns a boolean asserting whether an element is present with the given value in the set or not.

files/en-us/web/api/highlight/index.md

@@ -9,11 +9,11 @@ browser-compat: api.Highlight
 
 {{APIRef("CSS Custom Highlight API")}}{{SeeCompatTable}}
 
-The **`Highlight`** interface is used to represent a collection of {{domxref("Range")}} instances to be styled using the {{domxref("css_custom_highlight_api", "CSS Custom Highlight API", "", "nocode")}}.
+The **`Highlight`** interface of the [CSS Custom Highlight API](/en-US/docs/Web/API/CSS_Custom_Highlight_API) is used to represent a collection of {{domxref("Range")}} instances to be styled using the API.
 
 To style arbitrary ranges in a page, instantiate a new `Highlight` object, add one or more `Range` objects to it, and register it using the {{domxref("HighlightRegistry")}}.
 
-A single `Highlight` object can hold one or more `Range` objects and behaves like a {{jsxref("Set")}}.
+A single `Highlight` object is [`Set`-like object](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set#set-like_objects) that can hold one or more `Range` objects.
 
 {{InheritanceDiagram}}
 

files/en-us/web/api/highlightregistry/index.md

@@ -9,7 +9,10 @@ browser-compat: api.HighlightRegistry
 
 {{APIRef("CSS Custom Highlight API")}}{{SeeCompatTable}}
 
-The **`HighlightRegistry`** interface, accessed via {{domxref("CSS.highlights")}}, is a {{jsxref("Map")}}-like object used to register {{domxref("Highlight")}} objects to be styled using the {{domxref("css_custom_highlight_api", "CSS Custom Highlight API", "", "nocode")}}.
+The **`HighlightRegistry`** interface of the [CSS Custom Highlight API](/en-US/docs/Web/API/CSS_Custom_Highlight_API) is used to register {{domxref("Highlight")}} objects to be styled using the API.
+It is accessed via {{domxref("CSS.highlights")}}.
+
+`HighlightRegistry` is a [`Map`-like (or "maplike")](/en-US/docs/Glossary/Maplike_object) object, in which each key is the name string for a custom highlight, and the corresponding value is the associated {{domxref("Highlight")}} object.
 
 {{InheritanceDiagram}}
 

files/en-us/web/api/keyboardlayoutmap/index.md

@@ -9,7 +9,9 @@ browser-compat: api.KeyboardLayoutMap
 
 {{SeeCompatTable}}{{APIRef("Keyboard API")}}
 
-The **`KeyboardLayoutMap`** interface of the [Keyboard API](/en-US/docs/Web/API/Keyboard_API) is a map-like object with functions for retrieving the string associated with specific physical keys.
+The **`KeyboardLayoutMap`** interface of the [Keyboard API](/en-US/docs/Web/API/Keyboard_API) is a read-only object with functions for retrieving the string associated with specific physical keys.
+
+`KeyboardLayoutMap` is a read-only [`Map`-like object](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map#map-like_objects), in which each key is a string identifying the unique physical key on the keyboard (a "key code"), and the corresponding value is the associated key attribute value (which may be affected by the keyboard layout, and so on).
 
 A list of valid keys is found in the [UI Events KeyboardEvent code Values](https://www.w3.org/TR/uievents-code/#key-alphanumeric-writing-system) specification.
 

files/en-us/web/api/midiinputmap/index.md

@@ -7,7 +7,9 @@ browser-compat: api.MIDIInputMap
 
 {{APIRef("Web MIDI API")}}
 
-The **`MIDIInputMap`** read-only interface of the [Web MIDI API](/en-US/docs/Web/API/Web_MIDI_API) provides a {{jsxref('Map')}}-like interface to the currently available MIDI input ports. Though it works generally like a map, because it is read-only it does **not** contain `clear()`, `delete()`, or `set()` functions.
+The **`MIDIInputMap`** read-only interface of the [Web MIDI API](/en-US/docs/Web/API/Web_MIDI_API) provides the set of MIDI input ports that are currently available.
+
+`MIDIInputMap` is a read-only [`Map`-like object](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map#map-like_objects), in which each key is the ID string for MIDI input, and the associated value is the corresponding {{domxref("MIDIInput")}} object.
 
 ## Specifications
 

files/en-us/web/api/midioutputmap/index.md

@@ -7,7 +7,9 @@ browser-compat: api.MIDIOutputMap
 
 {{APIRef("Web MIDI API")}}
 
-The **`MIDIOutputMap`** read-only interface of the [Web MIDI API](/en-US/docs/Web/API/Web_MIDI_API) provides a {{jsxref('Map')}}-like interface to the currently available MIDI output ports. Although it works like a map, because it is read-only, it does **not** contain `clear()`, `delete()`, or `set()` functions.
+The **`MIDIOutputMap`** read-only interface of the [Web MIDI API](/en-US/docs/Web/API/Web_MIDI_API) provides the set of MIDI output ports that are currently available.
+
+`MIDIOutputMap` is a read-only [`Map`-like object](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map#map-like_objects), in which each key is the ID string for MIDI output, and the associated value is the corresponding {{domxref("MIDIOutput")}} object.
 
 ## Specifications
 

files/en-us/web/api/rtcstatsreport/index.md

@@ -9,7 +9,7 @@ browser-compat: api.RTCStatsReport
 
 The **`RTCStatsReport`** interface of the [WebRTC API](/en-US/docs/Web/API/WebRTC_API) provides a statistics report for a {{domxref("RTCPeerConnection")}}, {{domxref("RTCRtpSender")}}, or {{domxref("RTCRtpReceiver")}}.
 
-The report is a read-only [`Map`-like](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map) object, in which each key is an identifier for an object for which statistics are being reported, and the corresponding value is a dictionary object providing the statistics.
+The report is a read-only [`Map`-like object](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map#map-like_objects), in which each key is an identifier for an object for which statistics are being reported, and the corresponding value is a dictionary object providing the statistics.
 
 ## Instance properties
 

files/en-us/web/api/xranchorset/index.md

@@ -9,7 +9,7 @@ browser-compat: api.XRAnchorSet
 
 {{APIRef("WebXR Device API")}}{{SeeCompatTable}}
 
-The **`XRAnchorSet`** interface exposes a collection of anchors. It is returned by {{domxref("XRFrame.trackedAnchors")}} and is a {{jsxref("Set")}}-like object.
+The **`XRAnchorSet`** interface exposes a collection of anchors. It is returned by {{domxref("XRFrame.trackedAnchors")}} and is a [`Set`-like object](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set#set-like_objects) object.
 
 ## Instance properties
 

files/en-us/web/javascript/reference/global_objects/map/index.md

@@ -269,6 +269,40 @@ contacts.delete("Jessie"); // true
 console.log(contacts.size); // 1
 ```
 
+### Map-like objects
+
+**`Map`-like objects** (or "maplike objects") are browser-specific objects that behave in many ways like a `Map`.
+
+Just like `Map` they are ordered, and entries are iterated in the same sequence that they were added to the object, using all of the same looping constructs.
+`Map`-like objects also share some of the same properties and methods.
+However unlike `Map` they only allow specific predefined types for the keys and values of each entry.
+
+The allowed types are set in the specification IDL definition.
+For example, {{domxref("RTCStatsReport")}} is a `Map`-like object that must use strings for keys and any object as the value.
+This is defined in the specification IDL below:
+
+```webidl
+interface RTCStatsReport {
+  readonly maplike<DOMString, object>;
+};
+```
+
+`Map`-like objects are either read-only or read-writable (see the `readonly` keyword in the IDL above).
+
+- Read-only `Map`-like objects have the property [`size`](#map.prototype.size), and the methods: [`entries()`](#map.prototype.entries), [`forEach()`](#map.prototype.foreach), [`get()`](#map.prototype.get), [`has()`](#map.prototype.has), [`keys()`](#map.prototype.keys), [`values()`](#map.prototype.values), and [`@@iterator`](#map.prototypeiterator).
+- Writeable `Map`-like objects additionally have the methods: [`clear()`](#map.prototype.clear), [`delete()`](#map.prototype.delete), and [`set()`](#map.prototype.set).
+
+The methods and properties have the same behaviour as the equivalent entities in `Map`, except for the restriction on the types of the keys and values.
+
+The following items are examples of read-only `Map`-like objects:
+
+- {{domxref("AudioParamMap")}}
+- {{domxref("RTCStatsReport")}}
+- {{domxref("EventCounts")}}
+- {{domxref("KeyboardLayoutMap")}}
+- {{domxref("MIDIInputMap")}}
+- {{domxref("MIDIOutputMap")}}
+
 ## Constructor
 
 - {{jsxref("Map/Map", "Map()")}}

files/en-us/web/javascript/reference/global_objects/set/index.md

@@ -23,6 +23,42 @@ Value equality is based on the [SameValueZero](/en-US/docs/Web/JavaScript/Equali
 
 The [`has`](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set/has) method checks if a value is in the set, using an approach that is, on average, quicker than testing most of the elements that have previously been added to the set. In particular, it is, on average, faster than the [`Array.prototype.includes`](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/includes) method when an array has a `length` equal to a set's `size`.
 
+### Set-like objects
+
+**`Set`-like objects** (or "setlike objects") are browser-specific objects that behave in many ways like a [`Set`](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set).
+
+Just like `Set` they are ordered, and entries are iterated in the same sequence that they were added to the object, using all of the same looping constructs.
+`Set`-like objects also share some of the same properties and methods.
+However unlike `Set` they only allow a specific predefined type for each entry.
+
+The allowed types are set in the specification IDL definition.
+For example, {{domxref("GPUSupportedFeatures")}} is a `Set`-like object that must use strings as the key/value.
+This is defined in the specification IDL below:
+
+```webidl
+interface GPUSupportedFeatures {
+    readonly setlike<DOMString>;
+};
+```
+
+`Set`-like objects are either read-only or read-writable (see the `readonly` keyword in the IDL above).
+
+- Read-only `Set`-like objects have the property [`size`](#map.prototype.size), and the methods: [`entries()`](#map.prototype.entries), [`forEach()`](#map.prototype.foreach), [`has()`](#map.prototype.has), [`keys()`](#map.prototype.keys), [`values()`](#map.prototype.values), and [`@@iterator`](#map.prototypeiterator).
+- Writeable `Map`-like objects additionally have the methods: [`clear()`](#map.prototype.clear), [`delete()`](#map.prototype.delete), and [`add()`](#map.prototype.add).
+
+The methods and properties have the same behaviour as the equivalent entities in `Set`, except for the restriction on the types of the entry.
+
+The following interfaces are read-only `Set`-like objects:
+
+- {{domxref("GPUSupportedFeatures")}}
+- {{domxref("XRAnchorSet")}}
+
+The following interfaces are writable `Set`-like objects:
+
+- {{domxref("CustomStateSet")}}
+- {{domxref("FontFaceSet")}}
+- {{domxref("Highlight")}}
+
 ## Constructor
 
 - {{jsxref("Set/Set", "Set()")}}