HTML: The Living Standard
Edition for Web Developers — Last Updated 21 November 2024
Edition for Web Developers — Last Updated 21 November 2024
This standard contains several related concepts for grouping sequences of documents. As a brief, non-normative summary:
Navigables are a user-facing representation of a sequence
of documents, i.e., they represent something that can be navigated between documents. Typical
examples are tabs or windows in a web browser, or iframes.
Traversable navigables are a special type of navigable which control the session history of themselves and of their descendant navigables. That is, in addition to their own series of documents, they represent a tree of further series of documents, plus the ability to linearly traverse back and forward through a flattened view of this tree.
Browsing contexts are a developer-facing
representation of a series of documents. They correspond 1:1 with WindowProxy
objects. Each navigable can present a series of browsing contexts, with switches between
those browsing contexts occuring under certain well-defined circumstances.
Most of this standard works in the language of navigables, but certain APIs expose the existence of browsing context switches, and so some parts of the standard need to work in terms of browsing contexts.
A navigable presents a Document to the user via its active session history entry. Each navigable has:
An id, a new unique internal value.
A parent, a navigable or null.
A current session history entry, a session history entry.
This can only be modified within the session history traversal queue of the parent traversable navigable.
An active session history entry, a session history entry.
This can only be modified from the event loop of the active session history entry's document.
An is closing boolean, initially false.
This is only ever set to true for top-level traversable navigables.
An is delaying load
events boolean, initially false.
This is only ever set to true in cases where the navigable's parent is non-null.
The current session history entry and the active session history entry are usually the same, but they get out of sync when:
Synchronous navigations are performed. This causes the active session history entry to temporarily step ahead of the current session history entry.
A non-displayable, non-error response is received when applying the history step. This updates the current session history entry but leaves the active session history entry as-is.
A navigable's active document is its active session history entry's document.
This can be safely read from within the session history traversal queue of the
navigable's top-level traversable. Although a
navigable's active history entry can
change synchronously, the new entry will always have the same Document.
A navigable's active browsing context is its active document's browsing context. If this navigable is a traversable navigable, then its active browsing context will be a top-level browsing context.
A navigable's active WindowProxy is its
active browsing context's associated WindowProxy.
A navigable's active window
is its active WindowProxy's [[Window]].
This will always equal the navigable's active document's relevant global object; this is kept in sync by the make active algorithm.
A navigable's target name is its active session history entry's document state's navigable target name.
To get the node navigable of a node node, return the navigable whose active document is node's node document, or null if there is no such navigable.
To initialize the navigable navigable navigable, given a document state documentState and an optional navigable-or-null parent (default null):
Let entry be a new session history entry, with
The caller of this algorithm is responsible for initializing entry's
step; it will be left as "pending" until
that is complete.
Set navigable's current session history entry to entry.
Set navigable's active session history entry to entry.
Set navigable's parent to parent.
A traversable navigable is a navigable that also controls which session history entry should be the current session history entry and active session history entry for itself and its descendant navigables.
In addition to the properties of a navigable, a traversable navigable has:
A current session history step, a number, initially 0.
Session history entries, a list of session history entries, initially a new list.
A session history traversal queue, a session history traversal parallel queue, the result of starting a new session history traversal parallel queue.
A running nested apply history step boolean, initially false.
A system visibility state, which is either "hidden" or
"visible".
See the page visibility section for the requirements on this item.
To get the traversable navigable of a navigable inputNavigable:
Let navigable be inputNavigable.
While navigable is not a traversable navigable, set navigable to navigable's parent.
Return navigable.
A top-level traversable is a traversable navigable with a null parent.
Currently, all traversable navigables are top-level traversables. Future proposals envision introducing non-top-level traversables.
A user agent holds a top-level traversable set (a set of top-level traversables). These are typically presented to the user in the form of browser windows or browser tabs.
To get the top-level traversable of a navigable inputNavigable:
Let navigable be inputNavigable.
While navigable's parent is not null, set navigable to navigable's parent.
Return navigable.
To create a new top-level traversable given a browsing context-or-null opener, a string targetName, and an optional navigable openerNavigableForWebDriver:
Let document be null.
If opener is null, then set document to the second return value of creating a new top-level browsing context and document.
Otherwise, set document to the second return value of creating a new auxiliary browsing context and document given opener.
Let documentState be a new document state, with
Let traversable be a new traversable navigable.
Initialize the navigable traversable given documentState.
Let initialHistoryEntry be traversable's active session history entry.
Set initialHistoryEntry's step to 0.
Append initialHistoryEntry to traversable's session history entries.
If opener is non-null, then legacy-clone a traversable storage shed given opener's top-level traversable and traversable. [STORAGE]
Append traversable to the user agent's top-level traversable set.
Invoke WebDriver BiDi navigable created with traversable and openerNavigableForWebDriver.
Return traversable.
To create a fresh top-level traversable given a URL initialNavigationURL and an optional POST resource-or-null initialNavigationPostResource (default null):
Let traversable be the result of creating a new top-level traversable given null and the empty string.
Navigate traversable to initialNavigationURL using traversable's active document, with documentResource set to initialNavigationPostResource.
We treat these initial navigations as traversable navigating itself, which will ensure all relevant security checks pass.
Return traversable.
Certain elements (for example, iframe elements)
can present a navigable to the user. These elements are called navigable containers.
Each navigable container has a content navigable, which is either a navigable or null. It is initially null.
The container of a navigable navigable is the navigable container whose content navigable is navigable, or null if there is no such element.
The container document of a navigable navigable is the result of running these steps:
If navigable's container is null, then return null.
Return navigable's container's node document.
This is equal to navigable's container's shadow-including root as navigable's container has to be connected.
The container document of a Document
document is the result of running these steps:
If document's node navigable is null, then return null.
Return document's node navigable's container document.
A navigable navigable is a child navigable of another navigable potentialParent when navigable's parent is potentialParent. We can also just say that a navigable "is a child navigable", which means that its parent is non-null.
All child navigables are the content navigable of their container.
The content document of a navigable container container is the result of running these steps:
If container's content navigable is null, then return null.
Let document be container's content navigable's active document.
If document's origin and container's node document's origin are not same origin-domain, then return null.
Return document.
The content window of a navigable container container is the result of running these steps:
If container's content navigable is null, then return null.
Return container's content navigable's active WindowProxy's object.
To create a new child navigable, given an element element:
Let parentNavigable be element's node navigable.
Let group be element's node document's browsing context's top-level browsing context's group.
Let browsingContext and document be the result of creating a new browsing context and document given element's node document, element, and group.
Let targetName be null.
If element has a name content attribute, then set
targetName to the value of that attribute.
Let documentState be a new document state, with
Let navigable be a new navigable.
Initialize the navigable navigable given documentState and parentNavigable.
Set element's content navigable to navigable.
Let historyEntry be navigable's active session history entry.
Let traversable be parentNavigable's traversable navigable.
Append the following session history traversal steps to traversable:
Let parentDocState be parentNavigable's active session history entry's document state.
Let parentNavigableEntries be the result of getting session history entries for parentNavigable.
Let targetStepSHE be the first session history entry in parentNavigableEntries whose document state equals parentDocState.
Let nestedHistory be a new nested history whose id is navigable's id and entries list is « historyEntry ».
Append nestedHistory to parentDocState's nested histories.
Update for navigable creation/destruction given traversable.
Invoke WebDriver BiDi navigable created with traversable.
A useful method for visualizing sequences of documents, and in particular navigables and their session history entries, is the Jake diagram. A typical Jake diagram is the following:
| 0 | 1 | 2 | 3 | 4 | |
|---|---|---|---|---|---|
top | /t-a | /t-a#foo | /t-b | ||
frames[0] | /i-0-a | /i-0-b | |||
frames[1] | /i-1-a | /i-1-b | |||
Here, each numbered column denotes a possible value for the traversable's session history step. Each labeled row depicts a
navigable, as it transitions between different URLs and documents. The first,
labeled top, being the top-level traversable, and the others
being child navigables. The documents are given by the
background color of each cell, with a new background color indicating a new document in that
navigable. The URLs are given by the text content of the cells; usually they are
given as relative URLs for brevity, unless a cross-origin case
is specifically under investigation. A given navigable might not exist at a given step, in which
case the corresponding cells are empty. The bold-italic step number depicts the current session history step of the traversable,
and all cells with bold-italic URLs represent the current session history entry for that row's
navigable.
Thus, the above Jake diagram depicts the following sequence of events:
A top-level traversable is created, starting a the URL /t-a, with two child navigables
starting at /i-0-a and /i-1-a
respectively.
The first child navigable is navigated to another
document, with URL /i-0-b.
The second child navigable is navigated to another
document, with URL /i-1-b.
The top-level traversable is navigated to the
same document, updating its URL to /t-a#foo.
The top-level traversable is navigated to another
document, with URL /t-b. (Notice how this document, of course, does not
carry over the old document's child navigables.)
The traversable was traversed by a delta of −3, back to step 1.
Jake diagrams are a powerful tool for visualizing the interactions of multiple navigables, navigations, and traversals. They cannot capture every possible interaction — for example, they only work with a single level of nesting — but we will have ocassion to use them to illustrate several complex situations throughout this standard.
Jake diagrams are named after their creator, the inimitable Jake Archibald.
It is often helpful in this standard's algorithms to look at collections of navigables starting at a given Document. This section
contains a curated set of algorithms for collecting those navigables.
The return values of these algorithms are ordered so that parents appears before their children. Callers rely on this ordering.
Starting with a Document, rather than a navigable, is
generally better because it makes the caller cognizant of whether they are starting with a
fully active Document or not. Although non-fully active
Documents do have ancestor and descendant navigables, they often behave as if they
don't (e.g., in the window.parent getter).
The ancestor navigables of a Document
document are given by these steps:
Let navigable be document's node navigable's parent.
Let ancestors be an empty list.
While navigable is not null:
Return ancestors.
The inclusive ancestor navigables of a Document
document are given by these steps:
Let navigables be document's ancestor navigables.
Append document's node navigable to navigables.
Return navigables.
The descendant
navigables of a Document document are given by these steps:
Let navigables be new list.
Let navigableContainers be a list of all shadow-including descendants of document that are navigable containers, in shadow-including tree order.
For each navigableContainer of navigableContainers:
If navigableContainer's content navigable is null, then continue.
Extend navigables with navigableContainer's content navigable's active document's inclusive descendant navigables.
Return navigables.
The inclusive descendant navigables of a
Document document are given by these steps:
Let navigables be « document's node navigable ».
Extend navigables with document's descendant navigables.
Return navigables.
These descendant-collecting algorithms are described as looking at the DOM tree
of descendant Document objects. In reality, this is often not feasible since the DOM
tree can be in another process from the caller of the algorithm. Instead, implementations
generally replicate the appropriate trees across processes.
The document-tree child navigables of a
Document document are given by these steps:
If document's node navigable is null, then return the empty list.
Let navigables be new list.
Let navigableContainers be a list of all descendants of document that are navigable containers, in tree order.
For each navigableContainer of navigableContainers:
If navigableContainer's content navigable is null, then continue.
Append navigableContainer's content navigable to navigables.
Return navigables.
To destroy a child navigable given a navigable container container:
Let navigable be container's content navigable.
If navigable is null, then return.
Set container's content navigable to null.
Inform the navigation API about child navigable destruction given navigable.
Destroy a document and its descendants given navigable's active document.
Let parentDocState be container's node navigable's active session history entry's document state.
Remove the nested history from parentDocState's nested histories whose id equals navigable's id.
Let traversable be container's node navigable's traversable navigable.
Append the following session history traversal steps to traversable:
Update for navigable creation/destruction given traversable.
Invoke WebDriver BiDi navigable destroyed with navigable.
To destroy a top-level traversable traversable:
Let browsingContext be traversable's active browsing context.
For each historyEntry in traversable's session history entries in what order?:
Let document be historyEntry's document.
If document is not null, then destroy a document and its descendants given document.
Remove browsingContext.
Remove traversable from the user interface (e.g., close or hide its tab in a tabbed browser).
Remove traversable from the user agent's top-level traversable set.
Invoke WebDriver BiDi navigable destroyed with traversable.
User agents may destroy a top-level traversable at any time (typically, in response to user requests).
To close a top-level traversable traversable:
If traversable's is closing is true, then return.
Definitely close traversable.
To definitely close a top-level traversable traversable:
Let toUnload be traversable's active document's inclusive descendant navigables.
If the result of checking if unloading is canceled for toUnload is true, then return.
Append the following session history traversal steps to traversable:
Let afterAllUnloads be an algorithm step which destroys traversable.
Unload a document and its descendants given traversable's active document, null, and afterAllUnloads.
The close vs. definitely close separation allows other
specifications to call close and have it be a
no-op if the top-level traversable is already closing due to JavaScript code calling window.close().
Navigables can be given target
names, which are strings allowing certain APIs (such as window.open() or the a element's target attribute) to target navigations at that navigable.
A valid navigable target name is any string with at least one character that does not contain both an ASCII tab or newline and a U+003C (<), and it does not start with a U+005F (_). (Names starting with a U+005F (_) are reserved for special keywords.)
A valid navigable target name or
keyword is any string that is either a valid navigable target 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
navigable that the link or script is in, "parent" means the parent of the navigable that the link or script is in,
"top" means the top-level traversable of the navigable
that the link or script is in, "new" means a new traversable navigable with a null
parent (which may use an auxiliary browsing
context, 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.
| Keyword | Ordinary effect | Effect in an iframe with...
| |
|---|---|---|---|
sandbox=""
| sandbox="allow-top-navigation"
| ||
| none specified, for links and form submissions | current | current | current |
| empty string | current | current | current |
_blank
| new | maybe new | maybe new |
_self
| current | current | current |
_parent if there isn't a parent
| current | current | current |
_parent if parent is also top
| parent/top | none | parent/top |
_parent if there is one and it's not top
| parent | none | none |
_top if top is current
| current | current | current |
_top if top is not current
| top | none | top |
| name that doesn't exist | new | maybe new | maybe new |
| name that exists and is a descendant | specified descendant | specified descendant | specified descendant |
| name that exists and is current | current | current | current |
| name that exists and is an ancestor that is top | specified ancestor | none | specified ancestor/top |
| name that exists and is an ancestor that is not top | specified ancestor | none | none |
| other name that exists with common top | specified | none | none |
| name that exists with different top, if familiar and one permitted sandboxed navigator | specified | specified | specified |
| name that exists with different top, if familiar but not one permitted sandboxed navigator | specified | none | none |
| name that exists with different top, not familiar | new | maybe new | maybe new |
Most of the restrictions on sandboxed browsing contexts are applied by other algorithms, e.g. the navigation algorithm, not the rules for choosing a navigable given below.
The rules for choosing a navigable, given a string name, a navigable currentNavigable, and a boolean noopener are as follows:
Let chosen be null.
Let windowType be "existing or none".
Let sandboxingFlagSet be currentNavigable's active document's active sandboxing flag set.
If name is the empty string or an ASCII case-insensitive match
for "_self", then set chosen to
currentNavigable.
Otherwise, if name is an ASCII case-insensitive match for "_parent", set chosen to currentNavigable's parent, if any, and currentNavigable otherwise.
Otherwise, if name is an ASCII case-insensitive match for "_top", set chosen to currentNavigable's traversable navigable.
Otherwise, if name is not an ASCII case-insensitive match for "_blank", there exists a navigable whose target name is the same as name,
currentNavigable's active browsing context is
familiar with that navigable's active browsing
context, and the user agent determines that the two browsing contexts are related enough
that it is ok if they reach each other, set chosen to that navigable. If there are
multiple matching navigables, the user agent should pick one in
some arbitrary consistent manner, such as the most recently opened, most recently focused, or
more closely related, and set chosen to it.
This will be made more precise in issue #313.
Otherwise, a new top-level traversable is being requested, and what happens depends on the user agent's configuration and abilities — it is determined by the rules given for the first applicable option from the following list:
The user agent may inform the user that a popup has been blocked.
The user agent may report to a developer console that a popup has been blocked.
Consume user activation of currentNavigable's active window.
Set windowType to "new and unrestricted".
Let currentDocument be currentNavigable's active document.
If currentDocument's opener
policy's value is "same-origin" or "same-origin-plus-COEP", and
currentDocument's origin is not
same origin with currentDocument's relevant settings
object's top-level origin, then:
Set noopener to true.
Set name to "_blank".
Set windowType to "new with no opener".
In the presence of an opener policy, nested documents that are cross-origin with their top-level browsing context's active document always set noopener to true.
Let chosen be null.
Let targetName be the empty string.
If name is not an ASCII case-insensitive match for "_blank", then set targetName to name.
If noopener is true, then set chosen to the result of creating a new top-level traversable given null, targetName, and currentNavigable.
Otherwise:
Set chosen to the result of creating a new top-level traversable given currentNavigable's active browsing context, targetName, and currentNavigable.
If sandboxingFlagSet's sandboxed navigation browsing context flag is set, then set chosen's active browsing context's one permitted sandboxed navigator to currentNavigable's active browsing context.
If sandboxingFlagSet's sandbox propagates to auxiliary browsing contexts flag is set, then all the flags that are set in sandboxingFlagSet must be set in chosen's active browsing context's popup sandboxing flag set.
If the newly created navigable chosen is immediately
navigated, then the navigation will be done as a "replace" navigation.
Set chosen to currentNavigable.
Do nothing.
User agents are encouraged to provide a way for users to configure the user agent to always choose currentNavigable.
Return chosen and windowType.
A browsing context is a programmatic representation of a series of documents,
multiple of which can live within a single navigable. Each browsing
context has a corresponding WindowProxy object, as well as the following:
An opener browsing context, a browsing context or null, initially null.
An opener origin at creation, an origin or null, initially null.
An is popup boolean, initially false.
The only mandatory impact in this specification of is popup is on
the visible getter of the relevant
BarProp objects. However, user agents might also use it for user interface considerations.
An is auxiliary boolean, initially false.
An initial URL, a URL or null, initially null.
A virtual browsing context group ID integer, initially 0. This is used by 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'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.
A browsing context's top-level traversable is its active document's node navigable's top-level traversable.
A browsing context whose is auxiliary is true is known as an auxiliary browsing context. Auxiliary browsing contexts are always top-level browsing contexts.
It's unclear whether a separate is auxiliary concept is necessary. In issue #5680, it is indicated that we may be able to simplify this by using whether or not the opener browsing context is null.
Modern specifications should avoid using the
browsing context concept in most cases, unless they are dealing with the subtleties
of browsing context
group switches and agent cluster allocation. Instead,
the Document and navigable concepts are usually more appropriate.
A Document's browsing context is a browsing context or null,
initially null.
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 nulled out.
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, which will be done with replacement.
To create a new browsing context and document, given null or a Document
object creator, null or an element embedder, and a browsing context
group group:
Let browsingContext be a new browsing context.
Let unsafeContextCreationTime be the unsafe shared current time.
Let creatorOrigin be null.
Let creatorBaseURL be null.
If creator is non-null, then:
Set creatorOrigin to creator's origin.
Set creatorBaseURL to creator's document base URL.
Set browsingContext's virtual browsing context group ID to creator's browsing context's top-level browsing context's virtual browsing context group ID.
Let sandboxFlags be the result of determining the creation sandboxing flags given browsingContext and embedder.
Let origin be the result of determining the
origin given about:blank, sandboxFlags, and
creatorOrigin.
Let permissionsPolicy be the result of creating a permissions policy given embedder and origin. [PERMISSIONSPOLICY]
Let agent be the result of obtaining a similar-origin window agent given origin, group, and false.
Let realm execution context be the result of creating a new realm given agent and the following customizations:
For the global object, create a new Window object.
For the global this binding, use browsingContext's
WindowProxy object.
Let topLevelCreationURL be about:blank if embedder is
null; otherwise embedder's relevant settings object's top-level
creation URL.
Let topLevelOrigin be origin if embedder is null; otherwise embedder's relevant settings object's top-level origin.
Set up a window environment settings object with about:blank,
realm execution context, null, topLevelCreationURL, and
topLevelOrigin.
Let loadTimingInfo be a new document load timing info with its navigation start time set to the result of calling coarsen time with unsafeContextCreationTime and the new environment settings object's cross-origin isolated capability.
Let document be a new Document, with:
html"text/html"quirks"about:blankIf creator is non-null, then:
Set document's referrer to the serialization of creator's URL.
Set document's policy container to a clone of creator's policy container.
If creator's origin is same origin with creator's relevant settings object's top-level origin, then set document's opener policy to creator's browsing context's top-level browsing context's active document's opener policy.
Assert: document's URL
and document's relevant settings object's creation URL are
about:blank.
Mark document as ready for post-load tasks.
Populate with html/head/body given
document.
Make active document.
Completely finish loading document.
Return browsingContext and document.
To create a new top-level browsing context and document:
Let group and document be the result of creating a new browsing context group and document.
Return group's browsing context set[0] and document.
To create a new auxiliary browsing context and document, given a browsing context opener:
Let openerTopLevelBrowsingContext be opener's top-level traversable's active browsing context.
Let group be openerTopLevelBrowsingContext's group.
Assert: group is non-null, as navigating invokes this directly.
Let browsingContext and document be the result of creating a new browsing context and document with opener's active document, null, and group.
Set browsingContext's is auxiliary to true.
Append browsingContext to group.
Set browsingContext's opener browsing context to opener.
Set browsingContext's virtual browsing context group ID to openerTopLevelBrowsingContext's virtual browsing context group ID.
Set browsingContext's opener origin at creation to opener's active document's origin.
Return browsingContext and document.
To determine the origin, given a URL url, a sandboxing flag set sandboxFlags, and an origin-or-null sourceOrigin:
If sandboxFlags has its sandboxed origin browsing context flag set, then return a new opaque origin.
If url is null, then return a new opaque origin.
If url is about:srcdoc, then:
Assert: sourceOrigin is non-null.
Return sourceOrigin.
If url matches about:blank and
sourceOrigin is non-null, then return sourceOrigin.
Return url's origin.
The cases that return sourceOrigin result in two
Documents that end up with the same underlying origin, meaning that document.domain affects both.
A browsing context potentialDescendant is said to be an ancestor of a browsing context potentialAncestor if the following algorithm returns true:
Let potentialDescendantDocument be potentialDescendant's active document.
If potentialDescendantDocument is not fully active, then return false.
Let ancestorBCs be the list obtained by taking the browsing context of the active document of each member of potentialDescendantDocument's ancestor navigables.
If ancestorBCs contains potentialAncestor, then return true.
Return false.
A top-level browsing context is a browsing context whose active document's node navigable is a traversable navigable.
It is not required to be a top-level traversable.
The top-level browsing context of a browsing context start is the result of the following algorithm:
If start's active document is not fully active, then return null.
Let navigable be start's active document's node navigable.
While navigable's parent is not null, set navigable to navigable's parent.
Return navigable's active browsing context.
A browsing context A is familiar with a second browsing context B if the following algorithm returns true:
If A's active document's origin is same origin with B's active document's origin, then return true.
If A's top-level browsing context is B, then return true.
If B is an auxiliary browsing context and A is familiar with B's opener browsing context, then return true.
If there exists an ancestor browsing context of B whose active document has the same origin as the active document of A, then return true.
This includes the case where A is an ancestor browsing context of B.
Return false.
A top-level browsing context has an associated group (null or a browsing context group). It is initially null.
A user agent holds a browsing context group set (a set of browsing context groups).
A browsing context group holds a browsing context set (a set of top-level browsing contexts).
A top-level browsing context is added to the group when the group is created. All subsequent top-level browsing contexts added to the group will be auxiliary browsing contexts.
A browsing context group has an associated agent cluster map (a weak map of agent cluster keys to agent clusters). User agents are responsible for collecting agent clusters when it is deemed that nothing can access them anymore.
A browsing context group has an associated historical agent cluster key map, which is a map of origins to agent cluster keys. This map is used to ensure the consistency of the origin-keyed agent clusters feature by recording what agent cluster keys were previously used for a given origin.
The historical agent cluster key map only ever gains entries over the lifetime of the browsing context group.
A browsing context group has a cross-origin isolation mode, which is a
cross-origin isolation mode. It is initially "none".
A cross-origin isolation mode is one of three possible values: "none", "logical", or "concrete".
"logical" and "concrete" are similar. They are both used for
browsing context groups where:
every top-level Document has `Cross-Origin-Opener-Policy: same-origin`, and
every Document has a `Cross-Origin-Embedder-Policy` header
whose value is compatible with cross-origin isolation.
On some platforms, it is difficult to provide the security properties required to grant safe
access to the APIs gated by the cross-origin isolated
capability. As a result, only "concrete" can grant access that capability.
"logical" is used on platform not supporting
this capability, where various restrictions imposed by cross-origin isolation will still apply,
but the capability is not granted.
To create a new browsing context group and document:
Let group be a new browsing context group.
Append group to the user agent's browsing context group set.
Let browsingContext and document be the result of creating a new browsing context and document with null, null, and group.
Append browsingContext to group.
Return group and document.
To append a top-level browsing context browsingContext to a browsing context group group:
Append browsingContext to group's browsing context set.
Set browsingContext's group to group.
To remove a top-level browsing context browsingContext:
Let group be browsingContext's group.
Set browsingContext's group to null.
Remove browsingContext from group's browsing context set.
If group's browsing context set is empty, then remove group from the user agent's browsing context group set.
Append and remove are primitive operations that help define the lifetime of a browsing
context group. They are called by higher-level creation and destruction operations for
Documents and browsing contexts.
When there are no Document objects whose
browsing context equals a given browsing
context (i.e., all such Documents have been destroyed), and that browsing context's WindowProxy is
eligible for garbage collection, then the browsing context will never be accessed
again. If it is a top-level browsing context, then at this point the user agent must
remove it.
A Document d is said to be fully
active when d is the active document of a
navigable navigable, and either navigable is a top-level
traversable or navigable's container
document is fully active.
Because they are associated with an element, child
navigables are always tied to a specific Document, their container document, in their parent navigable. User agents must not allow the user to interact with
child navigables whose container documents are not themselves fully
active.
The following example illustrates how a Document can be the active document of its node navigable, while not being
fully active. Here a.html is loaded into a browser window,
b-1.html starts out loaded into an iframe as shown, and
b-2.html and c.html are omitted (they can simply
be an empty document).
<!-- a.html -->
<!DOCTYPE html>
< html lang = "en" >
< title > Navigable 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 > Navigable B</ title >
< iframe src = "c.html" ></ iframe > At this point, the documents given by a.html, b-1.html, and c.html are all the active documents of their respective node navigables. They are also all fully active.
After clicking on the button, and thus loading a new Document from
b-2.html into navigable B, we have the following results:
The a.html Document remains both the active document of navigable A, and fully
active.
The b-1.html Document is now not the active document of navigable B. As such it is also not fully
active.
The new b-2.html Document is now the active document of navigable B, and is also fully
active.
The c.html Document is still the active document of navigable C. However, since C's container document is the b-1.html Document, which is itself not fully active,
this means the c.html Document is now not fully
active.