Update groupdata of Picture-In-Picture API & some other update

files/en-us/web/api/picture-in-picture_api/index.md

@@ -16,6 +16,8 @@ The **Picture-in-Picture API** allow websites to create a floating, always-on-to
 
 - {{DOMxRef("PictureInPictureWindow")}}
   - : Represents the floating video window; contains {{domxref("PictureInPictureWindow/width", "width")}} and {{domxref("PictureInPictureWindow/height", "height")}} properties, and an {{domxref("PictureInPictureWindow/resize_event", "onresize")}} event handler property.
+- {{DOMxRef("PictureInPictureEvent")}}
+  - : Represents picture-in-picture-related events, including {{domxref("HTMLVideoElement/enterpictureinpicture_event", "enterpictureinpicture")}}, {{domxref("HTMLVideoElement/leavepictureinpicture_event", "leavepictureinpicture")}} and {{domxref("PictureInPictureWindow/resize_event", "resize")}}.
 
 ## Instance methods
 

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

@@ -7,7 +7,7 @@ browser-compat: api.PictureInPictureEvent
 
 {{APIRef("Picture-in-Picture API")}}
 
-The **`PictureInPictureEvent`** interface represents picture-in-picture-related events, including {{domxref("HTMLVideoElement/enterpictureinpicture_event", "enterpictureinpicture")}}, {{domxref("HTMLVideoElement/leavepictureinpicture_event", "leavepictureinpicture")}} and {{domxref("PictureInPictureWindow/resize_event", "resize")}}
+The **`PictureInPictureEvent`** interface represents picture-in-picture-related events, including {{domxref("HTMLVideoElement/enterpictureinpicture_event", "enterpictureinpicture")}}, {{domxref("HTMLVideoElement/leavepictureinpicture_event", "leavepictureinpicture")}} and {{domxref("PictureInPictureWindow/resize_event", "resize")}}.
 
 {{InheritanceDiagram}}
 

files/en-us/web/api/shadowroot/pictureinpictureelement/index.md

@@ -6,7 +6,7 @@ page-type: web-api-instance-property
 browser-compat: api.ShadowRoot.pictureInPictureElement
 ---
 
-{{APIRef("Shadow DOM")}}
+{{APIRef("Picture-in-Picture API")}}
 
 The **`pictureInPictureElement`** read-only property of the
 {{domxref("ShadowRoot")}} interface returns the {{domxref("Element")}} that is currently being
@@ -15,9 +15,9 @@ picture-in-picture mode is not currently in use.
 
 ## Value
 
-A reference to the {{domxref("Element")}} object that's currently in
-picture-in-picture mode, or, if picture-in-picture mode isn't currently in use by the
-shadow tree, the returned value is `null`.
+A reference to the {{domxref("Element")}} object that's currently in picture-in-picture mode.
+
+Returns `null` if the shadow tree has no associated element in picture-in-picture mode. For example, there's no picture-in-picture element, or the element is not in the shadow tree.
 
 ## Examples
 

files/jsondata/GroupData.json

@@ -1161,21 +1161,24 @@
     },
     "Picture-in-Picture API": {
       "overview": ["Picture-in-Picture API"],
-      "guides": ["/docs/Web/API/Picture-in-Picture_API/Guide"],
-      "interfaces": ["PictureInPictureWindow"],
+      "guides": [],
+      "interfaces": [
+        "PictureInPictureWindow",
+        "PictureInPictureEvent"
+      ],
       "methods": [
         "HTMLVideoElement.requestPictureInPicture()",
         "Document.exitPictureInPicture()"
       ],
       "properties": [
         "HTMLVideoElement.disablePictureInPicture",
         "Document.pictureInPictureEnabled",
-        "Document.pictureInPictureElement"
+        "Document.pictureInPictureElement",
+        "ShadowRoot.pictureInPictureElement"
       ],
       "events": [
         "HTMLVideoElement: enterpictureinpicture",
-        "HTMLVideoElement: leavepictureinpicture",
-        "PictureInPictureWindow: resize"
+        "HTMLVideoElement: leavepictureinpicture"
       ]
     },
     "Pointer Events": {