HTML: The Living Standard — Edition for Web Developers

Review Draft: search element with form functionality — Last Updated 1 December 2021

1. 7 Loading web pages
   1. 7.1 Browsing contexts
      1. 7.1.1 Creating browsing contexts
      2. 7.1.2 Related browsing contexts
         1. 7.1.2.1 Navigating related browsing contexts in the DOM
      3. 7.1.3 Browsing context names

7 Loading web pages

7.1 Browsing contexts

A browsing context is an environment in which Document objects are presented to the user.

A tab or window in a web browser typically contains a browsing context, as does an iframe.

A browsing context has a corresponding WindowProxy object.

A browsing context has an opener browsing context, which is null or a browsing context. It is initially null.

A browsing context has a disowned boolean. It is initially false.

A browsing context has an is closing boolean. It is initially false.

// Neither disowned nor is closing:
const popup1 = window.open();

// Disowned, but not is closing:
const popup2 = window.open();
popup2.opener = null;

// Not disowned, but is closing:
const popup3 = window.open();
popup3.close();

// Disowned, is closing:
const popup4 = window.open();
popup4.opener = null;
popup4.close();

A browsing context has a session history, which lists the Document objects that the browsing context has presented, is presenting, or will present. A Document's browsing context is the browsing context whose session history contains the Document, if any such browsing context exists and has not been discarded, and null otherwise.

A Document does not necessarily have a non-null browsing context. In particular, data mining tools are likely to never instantiate browsing contexts. A Document created using an API such as createDocument() never has a non-null browsing context. And the Document originally created for an iframe element, which has since been removed from the document, has no associated browsing context, since that browsing context was discarded.

A browsing context's active window is its WindowProxy object's [[Window]] internal slot value. A browsing context's active document is its active window's associated Document.

In general, there is a 1-to-1 mapping from the Window object to the Document object, as long as the Document object has a non-null browsing context. There is one exception. A Window can be reused for the presentation of a second Document in the same browsing context, such that the mapping is then 1-to-2. This occurs when a browsing context is navigated from the initial about:blank Document to another, with historyHandling set to "replace".

A browsing context has a virtual browsing context group ID integer. It is initially 0. This is used by cross-origin opener policy reporting, to keep track of the browsing context group switches that would have happened if the report-only policy had been enforced.

A browsing context has an initial URL, which is a URL or null. It is initially null.

A browsing context has an opener origin at creation, which is an origin or null. It is initially null.

7.1.1 Creating browsing contexts

To set the active document of a browsing context browsingContext to a Document object document, run these steps:

1. Let window be document's relevant global object.

2. Set document's visibility state to browsingContext's top-level browsing context's system visibility state.

3. Set browsingContext's active window to window.

4. Set window's associated Document to document.

5. Set window's relevant settings object's execution ready flag.

A browsing context has an associated creator origin (null or returns an origin), creator URL (null or returns a URL), and creator base URL (null or returns a URL). These are all initially null.

7.1.2 Related browsing contexts

Certain elements (for example, iframe elements) can instantiate further browsing contexts. These elements are called browsing context containers.

Each browsing context container has a nested browsing context, which is either a browsing context or null. It is initially null.

The container of a browsing context bc is the browsing context container whose nested browsing context is bc, or null if there is no such element.

Each browsing context bc has a container document, which is the result of running these steps:

1. If bc's container is null, then return null.

2. Return bc's container's node document.

   This is equal to bc's container's shadow-including root as bc's container has to be connected.

A browsing context child is said to be a child browsing context of another browsing context parent, if child's container document is non-null and child's container document's browsing context is parent.

A browsing context child is a document-tree child browsing context of parent if child is a child browsing context and child's container is in a document tree.

A browsing context child may have a parent browsing context. This is the unique browsing context that has child as a child browsing context, if any such browsing context exists. Otherwise, the browsing context has no parent browsing context.

A browsing context A is said to be an ancestor of a browsing context B if there exists a browsing context A' that is a child browsing context of A and that is itself an ancestor of B, or if the browsing context A is the parent browsing context of B.

A browsing context that has no parent browsing context is the top-level browsing context for itself and all of the browsing contexts for which it is an ancestor browsing context.

A top-level browsing context has an associated group (null or a browsing context group). It is initially null.

A top-level browsing context has an is popup boolean. It is initially false.

It is possible to create new browsing contexts that are related to a top-level browsing context while their container is null. Such browsing contexts are called auxiliary browsing contexts. Auxiliary browsing contexts are always top-level browsing contexts.

The transitive closure of parent browsing contexts for a browsing context that is a child browsing context gives the list of ancestor browsing contexts.

The list of the descendant browsing contexts of a Document d is the (ordered) list returned by the following algorithm:

1. Let list be an empty list.

2. For each browsing context container container, whose nested browsing context is non-null and whose shadow-including root is d, in shadow-including tree order:

   1. Let nestedBC be container's nested browsing context.

   2. Append nestedBC to list.

   3. Extend list with the list of the descendant browsing contexts of nestedBC's active document.

3. Return list.

A Document d is said to be fully active when d's browsing context is non-null, d's browsing context's active document is d, and either d's browsing context is a top-level browsing context, or d's browsing context's container document is fully active.

Because they are associated with an element, child browsing contexts are always tied to a specific Document in their parent browsing context. User agents must not allow the user to interact with child browsing contexts of elements that are in Documents that are not themselves fully active.

<!-- a.html -->
<!DOCTYPE html>
<html lang="en">
<title>Browsing context A</title>

<iframe src="b-1.html"></iframe>
<button onclick="frames[0].location.href = 'b-2.html'">Click me</button>

<!-- b-1.html -->
<!DOCTYPE html>
<html lang="en">
<title>Browsing context B</title>

<iframe src="c.html"></iframe>

A child browsing context can be put into a delaying load events mode. This is used when it is navigated, to delay the load event of its container before the new Document is created.

The document family of a browsing context consists of the union of all the Document objects in that browsing context's session history and the document families of all those Document objects. The document family of a Document object consists of the union of all the document families of the browsing contexts in the list of the descendant browsing contexts of the Document object.

The content document of a browsing context container container is the result of the following algorithm:

1. If container's nested browsing context is null, then return null.

2. Let context be container's nested browsing context.

3. Let document be context's active document.

4. If document's origin and container's node document's origin are not same origin-domain, then return null.

5. Return document.

7.1.2.1 Navigating related browsing contexts in the DOM

window.top

Returns the WindowProxy for the top-level browsing context.

window.opener [ = value ]

Returns the WindowProxy for the opener browsing context.

Returns null if there isn't one or if it has been set to null.

Can be set to null.

window.parent

Returns the WindowProxy for the parent browsing context.

window.frameElement

Returns the Element for the browsing context container.

Returns null if there isn't one, and in cross-origin situations.

7.1.3 Browsing context names

Browsing contexts can have a browsing context name. Unless stated otherwise, it is the empty string.

A valid browsing context name is any string with at least one character that does not start with a U+005F LOW LINE character. (Names starting with an underscore are reserved for special keywords.)

A valid browsing context name or keyword is any string that is either a valid browsing context name or that is an ASCII case-insensitive match for one of: _blank, _self, _parent, or _top.

These values have different meanings based on whether the page is sandboxed or not, as summarized in the following (non-normative) table. In this table, "current" means the browsing context that the link or script is in, "parent" means the parent browsing context of the one the link or script is in, "top" means the top-level browsing context of the one the link or script is in, "new" means a new top-level browsing context or auxiliary browsing context is to be created, subject to various user preferences and user agent policies, "none" means that nothing will happen, and "maybe new" means the same as "new" if the "allow-popups" keyword is also specified on the sandbox attribute (or if the user overrode the sandboxing), and the same as "none" otherwise.

Most of the restrictions on sandboxed browsing contexts are applied by other algorithms, e.g. the navigation algorithm, not the rules for choosing a browsing context given below.