This specification is like no other — it has been processed with you, the humble web developer, in mind.
The focus of this specification is readability and ease of access. Unlike the full HTML Standard, this "developer's edition" removes information that only browser vendors need know. It is automatically produced from the full specification by our build tooling, and thus always in sync with the latest developments in HTML.
To read about its conception, construction, and future, read the original press release, and the blog post about its relaunch.
Finally, feel free to contribute on GitHub to make this edition better for everyone!
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 a session history, which lists the
Document
objects that the browsing context has presented, is presenting,
or will present. A browsing context's active document is
its WindowProxy
object's [[Window]]
internal slot value's associated
Document
. 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.
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 browsing context. There are two exceptions. First, 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 replacement enabled.
Second, a Document
can end up being reused for several Window
objects
when the document.open()
method is used, such that the
mapping is then many-to-1.
A Document
does not necessarily have a browsing context associated with it. In particular, data
mining tools are likely to never instantiate browsing contexts. A Document
created
using an API such as createDocument()
never has a 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.
To set the active document of a browsing context
browsingContext to a Document
object document, optionally with
a Window
object window, run these steps:
If window is not given, let window be document's relevant global object.
Per this standard document can be created before window, which does not make much sense. See issue #2688.
Set browsingContext's WindowProxy
object's [[Window]] internal slot value to
window.
Set window's associated
Document
to document.
Set window's relevant settings object's execution ready flag.
A browsing context can have a creator browsing context, the browsing context that was responsible for its creation. If a browsing context has a parent browsing context, then that is its creator browsing context. Otherwise, if the browsing context has an opener browsing context, then that is its creator browsing context. Otherwise, the browsing context has no creator browsing context.
If a browsing context context has a creator browsing context creator, it also has the following properties. In what follows, let creator document be creator's active document at the time context is created:
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.
If a browsing context is the nested browsing context of a browsing context container, then the browsing context is said to be nested through the browsing context container's node document.
A browsing context child is said to be a child browsing context of another browsing context parent, if all of the following conditions hold:
child is a nested browsing context of a browsing context container element
element is connected
element's shadow-including root's browsing context is parent
A browsing context child is then a document-tree child browsing context of parent if it is a child browsing context and its browsing context container is not just connected, but also 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 is not a nested browsing context has no parent browsing context, and is the top-level browsing context of all the browsing contexts for which it is an ancestor browsing context.
The transitive closure of parent browsing contexts for a browsing context that is a nested 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:
Let list be an empty list.
For each child browsing context of d that is nested through an element that is in
the Document
d, in the tree order of the elements
nesting those browsing contexts, run these substeps:
Append that child browsing context to the list list.
Append the list of the descendant browsing contexts of the active document of that child browsing context to the list list.
Return the constructed list.
A Document
is said to be fully
active when it has a browsing context and it is
the active document of that browsing context, and either its browsing
context is a top-level browsing context, or it has a parent browsing
context and the Document
through which it is nested is itself
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 Document
s
that are not themselves fully active.
A browsing context that is a nested 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
browsing context 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 that are nested through the Document
object.
The content document of a browsing context container container is the result of the following algorithm:
If container's nested browsing context is null, then return null.
Let context be container's nested browsing context.
Let document be context's active document.
If document's origin and the origin specified by the current settings object are not same origin-domain, then return null.
Return document.
top
Returns the WindowProxy
for the top-level browsing context.
parent
Returns the WindowProxy
for the parent browsing context.
frameElement
Returns the Element
for the browsing context container.
Returns null if there isn't one, and in cross-origin situations.
It is possible to create new browsing contexts that are related to a top-level browsing context without being nested through an element. Such browsing contexts are called auxiliary browsing contexts. Auxiliary browsing contexts are always top-level browsing contexts.
An auxiliary browsing context has an opener browsing context, which is the browsing context from which the auxiliary browsing context was created.
The opener
IDL attribute on the Window
object, on getting, must return the WindowProxy
object of the browsing
context from which the current browsing context was created (its opener
browsing context), if there is one, if it is still available, and if the current
browsing context has not disowned its opener;
otherwise, it must return null. On setting, if the new value is null then the current
browsing context must disown its
opener; if the new value is anything else then the user agent must
call the [[DefineOwnProperty]] internal method of the Window
object, passing the
property name "opener
" as the property key, and the Property Descriptor {
[[Value]]: value, [[Writable]]: true, [[Enumerable]]: true,
[[Configurable]]: true } as the property descriptor,
where value is the new value.
If a browsing context has disowned its
opener, the value of its window.opener
is null
. That prevents scripts in the browsing context from changing
any properties of its opener browsing context's Window
(i.e., the window
from which the browsing context was created).
Otherwise, if a browsing context has not disowned its
opener, then scripts in that browsing context can use window.opener
to change properties of its opener browsing
context's Window
. For example, a script running in the browsing
context can change the value of window.opener.location
, causing the
opener browsing context to navigate to a completely different document.
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.
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 browsing context given below.