New page for HTMLInputElement.indeterminate (#35967)

* New page for HTMLInputElement.indeterminate

* Update index.md

* Update index.md

* Add links

* Update files/en-us/web/api/htmlinputelement/indeterminate/index.md

Co-authored-by: Joshua Chen <sidachen2003@gmail.com>

---------

Co-authored-by: Estelle Weyl <estelle@openwebdocs.org>

files/en-us/web/api/htmlinputelement/indeterminate/index.md

@@ -0,0 +1,47 @@
+---
+title: "HTMLInputElement: indeterminate property"
+short-title: indeterminate
+slug: Web/API/HTMLInputElement/indeterminate
+page-type: web-api-instance-property
+browser-compat: api.HTMLInputElement.indeterminate
+---
+
+{{APIRef("HTML DOM")}}
+
+The **`indeterminate`** property of the {{domxref("HTMLInputElement")}} interface returns a boolean value that indicates whether the checkbox is in the _indeterminate_ state. For example, a "select all/deselect all" checkbox may be in the indeterminate state when some but not all of its sub-controls are checked. The `indeterminate` state can only be set via JavaScript and is only relevant to [`checkbox`](/en-US/docs/Web/HTML/Element/input/checkbox) controls.
+
+It is unrelated to the {{domxref("HTMLInputElement.checked")}} property, and an indeterminate checkbox can be either checked or unchecked. Being indeterminate only affects the checkbox's appearance (see example below), not its presence when submitted (which is controlled by the checkedness).
+
+## Value
+
+A boolean.
+
+## Examples
+
+```html
+<input type="checkbox" id="indeterminate-checkbox" />
+<label for="indeterminate-checkbox">Indeterminate checkbox</label>
+```
+
+```js
+const checkbox = document.getElementById("indeterminate-checkbox");
+checkbox.indeterminate = true;
+```
+
+{{EmbedLiveSample("examples", "", 200)}}
+
+## Specifications
+
+{{Specifications}}
+
+## Browser compatibility
+
+{{Compat}}
+
+## See also
+
+- {{domxref("HTMLInputElement")}}
+- {{domxref("HTMLInputElement.checked")}}
+- {{HTMLElement("input")}}
+- [Indeterminate state checkboxes](/en-US/docs/Web/HTML/Element/input/checkbox#indeterminate_state_checkboxes)
+- CSS {{cssxref(":indeterminate")}} property

files/en-us/web/css/_colon_indeterminate/index.md

@@ -7,7 +7,7 @@ browser-compat: css.selectors.indeterminate
 
 {{CSSRef}}
 
-The **`:indeterminate`** [CSS](/en-US/docs/Web/CSS) [pseudo-class](/en-US/docs/Web/CSS/Pseudo-classes) represents any form element whose state is indeterminate, such as checkboxes that have been set to an [`indeterminate`](/en-US/docs/Web/HTML/Element/input/checkbox#indeterminate_state_checkboxes) state with JavaScript, radio buttons which are members of a group in which all radio buttons are unchecked, and {{HTMLElement("progress")}} elements with no `value` attribute.
+The **`:indeterminate`** [CSS](/en-US/docs/Web/CSS) [pseudo-class](/en-US/docs/Web/CSS/Pseudo-classes) represents any form element whose state is indeterminate, such as checkboxes that have been set to an [`indeterminate`](/en-US/docs/Web/API/HTMLInputElement/indeterminate) state with JavaScript, radio buttons which are members of a group in which all radio buttons are unchecked, and {{HTMLElement("progress")}} elements with no `value` attribute.
 
 ```css
 /* Selects any <input> whose state is indeterminate */
@@ -18,7 +18,7 @@ input:indeterminate {
 
 Elements targeted by this selector are:
 
-- [`<input type="checkbox">`](/en-US/docs/Web/HTML/Element/input/checkbox) elements whose `indeterminate` property is set to `true` by [JavaScript](/en-US/docs/Web/JavaScript)
+- [`<input type="checkbox">`](/en-US/docs/Web/HTML/Element/input/checkbox) elements whose [`indeterminate`](/en-US/docs/Web/API/HTMLInputElement/indeterminate) property is set to `true`
 - [`<input type="radio">`](/en-US/docs/Web/HTML/Element/input/radio) elements, when all radio buttons with the same `name` value in the form are unchecked
 - {{HTMLElement("progress")}} elements in an indeterminate state
 
@@ -131,6 +131,6 @@ progress:indeterminate {
 
 - [Web forms — Working with user data](/en-US/docs/Learn/Forms)
 - [Styling web forms](/en-US/docs/Learn/Forms/Styling_web_forms)
-- The [`<input type="checkbox">`](/en-US/docs/Web/HTML/Element/input/checkbox) element's [`indeterminate`](/en-US/docs/Web/HTML/Element/input/checkbox#indeterminate_state_checkboxes) property
+- The [`<input type="checkbox">`](/en-US/docs/Web/HTML/Element/input/checkbox) element's [`indeterminate`](/en-US/docs/Web/API/HTMLInputElement/indeterminate) property
 - {{HTMLElement("input")}} and the {{domxref("HTMLInputElement")}} interface which implements it.
 - The {{cssxref(":checked")}} CSS selector lets you style checkboxes based on whether they're checked or not

files/en-us/web/html/element/input/checkbox/index.md

@@ -111,7 +111,7 @@ Beyond accessibility, this is another good reason to properly set up `<label>` e
 
 ### Indeterminate state checkboxes
 
-A checkbox can be in an **indeterminate** state. This is set using the {{domxref("HTMLInputElement")}} object's `indeterminate` property via JavaScript (it cannot be set using an HTML attribute):
+A checkbox can be in an **indeterminate** state. This is set using the {{domxref("HTMLInputElement")}} object's [`indeterminate`](/en-US/docs/Web/API/HTMLInputElement/indeterminate) property via JavaScript (it cannot be set using an HTML attribute):
 
 ```js
 inputInstance.indeterminate = true;