1. Infrastructure
This specification depends on the Infra Standard. [INFRA]
2. Introduction
2.1. Use cases
2.1.1. Web text references
The core use case for text fragments is to allow URLs to serve as an exact text reference across the web. For example, Wikipedia references could link to the exact text they are quoting from a page. Similarly, search engines can serve URLs that direct the user to the answer they are looking for in the page rather than linking to the top of the page.2.1.2. User sharing
With text fragments, browsers may implement an option to 'Copy URL to here' when the user opens the context menu on a text selection. The browser can then generate a URL with the text selection appropriately specified, and the recipient of the URL will have the specified text conveniently indicated. Without text fragments, if a user wants to share a passage of text from a page, they would likely just copy and paste the passage, in which case the receiver loses the context of the page.3. Description
3.1. Indication
This specification intentionally doesn’t define what actions a user agent should or could take to "indicate" a text match. There are different experiences and trade-offs a user agent could make. Some examples of possible actions:
-
Providing visual emphasis or highlight of the text passage
-
Automatically scrolling the passage into view when the page is navigated
-
Activating a UA’s find-in-page feature on the text passage
-
Providing a "Click to scroll to text passage" notification
-
Providing a notification when the text passage isn’t found in the page
3.2. Syntax
A text fragment directive is specified in the fragment directive (see § 3.3 The Fragment Directive) with the following format:
#:~:text=[prefix-,]textStart[,textEnd][,-suffix] context |-------match-----| context
(Square brackets indicate an optional parameter)
The text parameters are percent-decoded before matching. Dash (-), ampersand (&), and comma (,) characters in text parameters must be percent-encoded to avoid being interpreted as part of the text directive syntax.
The only required parameter is textStart. If only textStart is specified, the first instance of this exact text string is the target text.
#:~:text=an%20example%20text%20fragment
indicates that the
exact text "an example text fragment" is the target text. If the textEnd parameter is also specified, then the text directive refers to a range of text in the page. The target text range is the text range starting at the first instance of textStart, until the first instance of textEnd that appears after textStart. This is equivalent to specifying the entire text range in the textStart parameter, but allows the URL to avoid being bloated with a long text directive.
#:~:text=an%20example,text%20fragment
indicates that the first
instance of "an example" until the following first instance of "text fragment"
is the target text. 3.2.1. Context Terms
The other two optional parameters are context terms. They are specified by the dash (-) character succeeding the prefix and preceding the suffix, to differentiate them from the textStart and textEnd parameters, as any combination of optional parameters may be specified.
Context terms are used to disambiguate the target text fragment. The context terms can specify the text immediately before (prefix) and immediately after (suffix) the text fragment, allowing for whitespace.
The context terms are not part of the targeted text fragment and must not be visually indicated.
#:~:text=this%20is-,an%20example,-text%20fragment
would match
to "an example" in "this is an example text fragment", but not match to "an
example" in "here is an example text". 3.2.2. BiDi Considerations
Since URL strings are ASCII encoded, they provide no built-in support for bi-directional text. However, the content that we wish to target on a page may be LTR (left-to-right), RTL (right-to-left) or both (Bidirectional/BiDi). This section provides an intuitive description the behavior implicitly described by the normative sections further in this spec.
The characters of each term in the text fragment are in logical order, that is, the order in which a native reader would read them in (and also the order in which characters are stored in memory).
Similarly, the prefix
and textStart
terms identify
text coming before another term in logical order, while suffix
and textEnd
follow other terms in logical order.
Note: user agents may visually render URLs in a manner friendlier to a native reader, for example, by converting the displayed string to Unicode. However, the string representation of a URL remains plain ASCII characters.
مِصر
(Egypt, in Arabic),
that’s preceeded by البحرين
(Bahrain, in Arabic). We would
first percent encode each term:
مِصر
becomes "%D9%85%D8%B5%D8%B1" (Note: UTF-8 character
[0xD9,0x85] is the first (right-most) character of the Arabic word.)
البحرين
becomes "%D8%A7%D9%84%D8%A8%D8%AD%D8%B1%D9%8A%D9%86"
The text fragment would then become:
:~:text=%D8%A7%D9%84%D8%A8%D8%AD%D8%B1%D9%8A%D9%86-,%D9%85%D8%B5%D8%B1
When displayed in a browser’s address bar, the browser may visually render the text in its natural RTL direction, appearing to the user:
:~:text=البحرين-,مِصر
3.3. The Fragment Directive
To avoid compatibility issues with usage of existing URL fragments, this spec introduces the fragment directive. The fragment directive is a portion of the URL fragment that follows the fragment directive delimiter.
The fragment directive delimiter is the string ":~:", that is the three consecutive code points U+003A (:), U+007E (~), U+003A (:).
The fragment directive is meant to carry instructions, such as text=
, for the UA rather than for the document.
To prevent impacting page operation, it is stripped from a Document's URL so that author scripts can’t directly interact with it. This also ensures future directives could be added without introducing breaking changes to existing content. Potential examples could be: image-fragments, translation-hints.
3.3.1. Processing the fragment directive
The fragment directive is processed and removed from the fragment whenever the UA sets the URL on a Document. This is defined with the following additions and changes.
To the definition of Document, add:
Monkeypatching [DOM]:
Each document has an associated fragment directive which is either null or an ASCII string holding data used by the UA to process the resource. It is initially null.
Whenever the fragment directive is stripped from the URL, it is set to the Document’s fragment directive.
Add a series of steps that will process a fragment directive on a URL:
Monkeypatching [DOM]:
To process and consume fragment directive from a URL url and Document document, run these steps:
Let raw fragment be equal to url’s fragment.
If raw fragment is non-null and contains the fragment directive delimiter as a substring:
Let fragmentDirectivePosition be the index of the first instance of the fragment directive delimiter in raw fragment.
Let fragment be the substring of raw fragment starting at 0 of count fragmentDirectivePosition.
Advance fragmentDirectivePosition by the length of fragment directive delimiter.
Let fragment directive be the substring of raw fragment starting at fragmentDirectivePosition.
Set url’s fragment to fragment.
Set document’s fragment directive to fragment directive.
This is stored on the document but currently not web-exposed
https://example.org/#test:~:text=foo
will be parsed such that
the fragment is the string "test" and the fragment directive is the string
"text=foo". Amend the create and initialize a Document object steps to parse and remove the fragment directive by inserting the following steps right before the setting document’s URL (currently step 9):
Monkeypatching [HTML]:
Run the process and consume fragment directive steps on creationURL and document.
Set document’s URL to be creationURL.
Amend the traverse the history steps to process the fragment directive during a history navigation by inserting steps before setting the newDocument’s URL (currently step 6).
Monkeypatching [HTML]:
Let processedURL be a copy of entry’s URL.
Run the process and consume fragment directive steps on processedURL and document.
Set newDocument’s URL to processedURL.
The changes in this section imply that a URL is only stripped of its fragment
directive when it is set on a Document. Notably, since a window’s Location
object is a representation of the URL of the active
document, all getters on it will show a fragment-directive-stripped
version of the URL.
Some examples should help clarify various edge cases.
window.location = 'https://example.com#foo:~:bar';
The page loads and when the document’s URL is set the fragment directive is stripped out during the "create and initialize a Document object" steps.
console.log(window.location.href); // 'https://example.com#foo' console.log(window.location.hash); // '#foo'
Since same document navigations are made by adding a new session history entry and using the "traverse the history" steps, the the fragment directive will be stripped here as well.
window.location.hash = 'fizz:~:buzz'; console.log(window.location.href); // 'https://example.com#fizz' console.log(window.location.hash); // '#fizz'
The hashchange event is dispatched when only the fragment directive changes because the comparison for it is done on the URLs in the session history entries, where the fragment directive hasn’t been removed.
onhashchange = () => {console.log('HASHCHANGE');}; window.location.hash = 'fizz:~:zillch'; // 'HASHCHANGE' console.log(window.location.href); // 'https://example.com#fizz' console.log(window.location.hash); // '#fizz'
For URL objects:
let url = new URL('https://example.com#foo:~:bar'); console.log(url.href); // 'https://example.com#foo:~:bar' console.log(url.hash); // '#foo:~:bar' document.url = url; console.log(document.url.href); // 'https://example.com#foo:~:bar' console.log(document.url.hash); // '#foo:~:bar'
The <a>
or <area>
elements:
<a id='anchor' href="https://example.com#foo:~:bar">Anchor</a> <script> console.log(anchor.href); // 'https://example.com#foo:~:bar' console.log(anchor.hash); // '#foo:~:bar' </script>
history.pushState({}, 'title', 'index.html#foo:~:bar'); window.location = 'newpage.html'; // on newpage.html history.back();
Results in the current document having "bar" as the fragment directive.
3.3.2. Parsing the fragment directive
A ParsedTextDirective is a struct that consists of four strings: textStart, textEnd, prefix, and suffix. textStart is required to be non-null. The other three items may be set to null, indicating they weren’t provided. The empty string is not a valid value for any of these items.
See § 3.2 Syntax for the what each of these components means and how they’re used.
To parse a text directive, on an ASCII string text directive input, run these steps:
This algorithm takes a single text directive string as input (e.g. "text=prefix-,foo,bar") and attempts to parse the string into the components of the directive (e.g. ("prefix", "foo", "bar", null)). See § 3.2 Syntax for the what each of these components means and how they’re used.
Returns null if the input is invalid or fails to parse in any way. Otherwise, returns a ParsedTextDirective.
-
Assert: text directive input matches the production TextDirective.
-
Let textDirectiveString be the substring of text directive input starting at index 5.
This is the remainder of the text directive input following, but not including, the "text=" prefix. -
Let tokens be a list of strings that is the result of splitting textDirectiveString on commas.
-
If tokens has size less than 1 or greater than 4, return null.
-
If any of tokens’s items are the empty string, return null.
-
Let retVal be a ParsedTextDirective with each of its items initialized to null.
-
Let potential prefix be the first item of tokens.
-
If the last character of potential prefix is U+002D (-), then:
-
Set retVal’s prefix to the percent-decoding of the result of removing the last character from potential prefix.
-
Remove the first item of the list tokens.
-
-
Let potential suffix be the last item of tokens, if one exists, null otherwise.
-
If potential suffix is non-null and its first character is U+002D (-), then:
-
Set retVal’s suffix to the percent-decoding of the result of removing the first character from potential suffix.
-
Remove the last item of the list tokens.
-
-
If tokens has size not equal to 1 nor 2 then return null.
-
Set retVal’s textStart be the percent-decoding of the first item of tokens.
-
If tokens has size 2, then set retVal’s textEnd be the percent-decoding of the last item of tokens.
-
Return retVal.
3.3.3. Fragment directive grammar
A valid fragment directive is a sequence of characters that appears in the fragment directive that matches the production:
-
FragmentDirective
::=
-
(TextDirective | UnknownDirective) ("&" FragmentDirective)?
-
UnknownDirective
::=
-
CharacterString
-
CharacterString
::=
-
(ExplicitChar | PercentEncodedChar)+
-
ExplicitChar
::=
-
[a-zA-Z0-9] | "!" | "$" | "'" | "(" | ")" | "*" | "+" | "." | "/" | ":" | ";" | "=" | "?" | "@" | "_" | "~" | "&" | "," | "-"
An ExplicitChar may be any URL code point.
The text fragment directive is one such fragment directive that enables specifying a piece of text on the page, that matches the production:
TextDirective
::=
"text=" TextDirectiveParameters
TextDirectiveParameters
::=
-
(TextDirectivePrefix ",")? TextDirectiveString ("," TextDirectiveString)? ("," TextDirectiveSuffix)?
TextDirectivePrefix
::=
TextDirectiveString"-"
TextDirectiveSuffix
::=
"-"TextDirectiveString
TextDirectiveString
::=
(TextDirectiveExplicitChar | PercentEncodedChar)+
TextDirectiveExplicitChar
::=
-
[a-zA-Z0-9] | "!" | "$" | "'" | "(" | ")" | "*" | "+" | "." | "/" | ":" | ";" | "=" | "?" | "@" | "_" | "~"
A TextDirectiveExplicitChar may be any URL code point that is not explicitly used in the TextDirective syntax, that is "&", "-", and ",", which must be percent-encoded. PercentEncodedChar
::=
"%" [a-zA-Z0-9]+
3.4. Security and Privacy
3.4.1. Motivation
Care must be taken when implementing text fragment directive so that it cannot be used to exfiltrate information across origins. Scripts can navigate a page to a cross-origin URL with a text fragment directive. If a malicious actor can determine that the text fragment was successfully found in victim page as a result of such a navigation, they can infer the existence of any text on the page.
The following subsections restrict the feature to mitigate the expected attack vectors. In summary, the text fragment directives are invoked only on full (non-same-page) navigations that are the result of a user activation. Additionally, navigations originating from a different origin than the destination will require the navigation to take place in a "noopener" context, such that the destination page is known to be sufficiently isolated.
3.4.2. Scroll On Navigation
A UA may choose to automatically scroll a matched text passage into view. This can be a convenient experience for the user but does present some risks that implementing UAs should be aware of.
There are known (and potentially unknown) ways a scroll on navigation might be detectable and distinguished from natural user scrolls.
All known cases like this rely on specific circumstances about the target page so don’t apply generally. With additional restrictions about when the text fragment can invoke an attacker is further restricted. Nonetheless, different UAs can come to different conclusions about whether these risks are acceptable. UAs should consider these factors when determining whether to scroll as part of navigating to a text fragment.
Conforming UAs may choose not to scroll automatically on navigation. Such UAs may, instead, provide UI to initiate the scroll ("click to scroll") or none at all. In these cases UA should provide some indication to the user that an indicated passage exists further down on the page.
The examples above illustrate that in specific circumstances, it may be possible for an attacker to extract 1 bit of information about content on the page. However, care must be taken so that such opportunities cannot be exploited to extract arbitrary content from the page by repeating the attack. For this reason, restrictions based on user activation and browsing context isolation are very important and must be implemented.
However, it also ensures any malicious use is difficult to hide. A browsing context that’s the only one in a group must be a top level browsing context (i.e. a full tab/window).
If a UA does choose to scroll automatically, it must ensure no scrolling is performed while the document is in the background (for example, in an inactive tab). This ensures any malicious usage is visible to the user and prevents attackers from trying to secretly automate a search in background documents.
3.4.3. Search Timing
A naive implementation of the text search algorithm could allow information exfiltration based on runtime duration differences between a matching and non- matching query. If an attacker could find a way to synchronously navigate to a text fragment directive-invoking URL, they would be able to determine the existence of a text snippet by measuring how long the navigation call takes.
For this reason, the implementation must ensure the runtime of § 3.5 Navigating to a Text Fragment steps does not differ based on whether a match has been successfully found.
This specification does not specify exactly how a UA achieves this as there are multiple solutions with differing tradeoffs. For example, a UA may continue to walk the tree even after a match is found in find a range from a text directive. Alternatively, it may schedule an asynchronous task to find and set the indicated part of the document.
3.4.4. Restricting the Text Fragment
Amend the definition of a request and of a Document to include a new field for the textFragmentToken:
Monkeypatching [FETCH]:
A request has an associated textFragmentToken flag
Monkeypatching [HTML]:
A Document has a textFragmentToken flag that is consumed in order to allow a single activation of a text fragment. This flag is generated only during loading if the navigation occurs as a result of a user activation.
If the Document's textFragmentToken isn’t consumed to activate a text fragment, it may be consumed to set the textFragmentToken flag of a navigation request. In this way, a textFragmentToken can be propagated from one Document to another across a navigation.
Reading either the Document's textFragmentToken or the request's textFragmentToken must always consume the value, such that the token cannot be cloned.
A textFragmentToken is generated when a Document is loaded as a result of a user gesture. It grants its holder permission (in terms of user activation) to activate a single text fragment. Alternatively, it may be propagated through a navigation to allow a future document to activate a text fragment from this navigation’s user gesture.
This mechanism allows text fragments to activate through a common redirect technique used my many popular web sites. Such sites redirect users to their intended destination by responding with a 200 status code containing script to set the window.location .
Unlike real HTTP ( status 3xx ) redirects, these "client-side" redirects cannot propagate the fact that the navigation is the result of a user gesture. The textFragmentToken mechanism allows passing through this specifically scoped user-activation through such navigations. This means a page can programmatically navigate to a text fragment, a single time, as if it has a user gesture. However, further navigations require a new user gesture.
The following diagram demonstrates how the token is used to activate a text fragment through a client-side redirect service:

See redirects.md for a more in-depth discussion.
Monkeypatching [HTML]:
A Document has an allowTextFragmentDirective flag that is used to determine whether a text fragment directive should be allowed to activate. If this flag is false, the text fragment must not cause any observable effects.
textFragmentToken is analogous to a user-activation state while allowTextFragmentDirective is more comprehensive, taking into account various pieces of information, one of which is the existence of a textFragmentToken.
The reason we compute allowTextFragmentDirective and keep it as a flag, rather than performing the checks at the time of use, is that it relies on the properties of the navigation while the invocation will occur as part of the scroll to the fragment steps which can happen outside the context of a navigation.
Amend the create and initialize a Document object steps by adding the following steps before returning document:
Monkeypatching [HTML]:
Set the textFragmentToken flag on document:
Let is user activated be true if the current navigation was initiated from a window that had a transient activation at the time the navigation was initiated, or the UA has reason to believe it comes from a direct user gesture (e.g. user typed into the address bar).
TODO: it’d be better to refer to the userActivationFlag on the request. See Sec-Fetch-User in [FETCH-METADATA].If browsing context is a top-level browsing context and if either of is user activated or the textFragmentToken flag of navigationParam’s request object is true, set the document’s textFragmentToken flag to true. Otherwise, set it to false.
It’s important that the token not be copyable so that at most one token is created per user-activated navigation.Set the allowTextFragmentDirective flag on document by following these sub-steps:
If document’s fragment directive field is null or empty, set allowTextFragmentDirective to false and abort these sub-steps.
Let textFragmentToken be the value of document’s textFragmentToken and set document’s textFragmentToken to false.
If the navigationParam’s request has a sec-fetch-site header and its value is
"none"
set allowTextFragmentDirective to true and abort these sub-steps.If a navigation originates from browser UI, it’s always ok to allow it since it’ll be user triggered and the page/script isn’t providing the text snippet.
Note: Depending on the UA, there may be cases where the incumbentNavigationOrigin parameter is null but it’s not clear that the navigation should be considered as initiated from browser UI. E.g. an "open in new window" context menu item when right clicking on a link. The intent in this item is to distinguish cases where the app/page is able to set the URL from those that are fully under the user’s control. In the former we want to prevent activation of the text fragment unless the destination is loaded in a separate browsing context group (so that the source cannot both control the text snippet and observe side-effects in the navigation).
See sec-fetch-site for a more detailed discussion of how this should apply.
If textFragmentToken is false, set allowTextFragmentDirective to false and abort these sub-steps.
If the document of the latest entry in document’s browsing context's session history is equal to document, set allowTextFragmentDirective to false and abort these sub-steps.
i.e. Forbidden on a same-document navigation.If the navigationParam’s request has a sec-fetch-site header and its value is
"same-origin"
set allowTextFragmentDirective to true and abort these sub-steps.If document’s browsing context is a top-level browsing context and its group’s browsing context set has length 1, set allowTextFragmentDirective to true and abort these sub-steps.
i.e. Only allow navigation from a cross-origin element/script if the document is loaded in a noopener context. That is, a new top level browsing context group to which the navigator does not have script access and which may be placed into a separate process.Otherwise, set allowTextFragmentDirective to false.
Amend step 2 of the process a navigate fetch steps to additionally set request’s textFragmentToken to the value of the active document's textFragmentToken and set the active document's value to false.
Monkeypatching [HTML]:
Set request’s client to sourceBrowsingContext’s active document’s relevant settings object, destination to "document", mode to "navigate", credentials mode to "include", use-URL-credentials flag, redirect mode to "manual", replaces client id to browsingContext’s active document’s relevant settings object’s id, and textFragmentToken to sourceBrowsingContext’s active document’s textFragmentToken. Set sourceBrowsingContext’s active document’s textFragmentToken to false.
Amend the try to scroll to the fragment steps by replacing the steps of the task queued in step 2:
Monkeypatching [HTML]:
If document has no parser, or its parser has stopped parsing, or the user agent has reason to believe the user is no longer interested in scrolling to the fragment, then clear document’s allowTextFragmentDirective flag and abort these steps.
Scroll to the fragment given in document’s URL. If this does not find an indicated part of the document, then try to scroll to the fragment for document.
Clear document’s allowTextFragmentDirective flag
3.5. Navigating to a Text Fragment
Replace step 3.1 of the scroll to the fragment algorithm with the following:
Monkeypatching [HTML]:
Let target, range be the element and range that is the indicated part of the document.
Replace step 3.3 of the scroll to the fragment algorithm with the following:
Monkeypatching [HTML]:
Get the policy value for
force-load-at-top
in the Document. If the result is true, abort these steps.If range is non-null:
If the UA supports scrolling of text fragments on navigation, invoke Scroll range into view, with range range, containingElement target, behavior set to "auto", block set to "center", and inline set to "nearest".
Otherwise:
Scroll target into view, with behavior set to "auto", block set to "start", and inline set to "nearest".
This otherwise case is the same as the current step 3.3.
Add the following steps to the beginning of the processing model for the indicated part of the document:
Monkeypatching [HTML]:
Let fragment directive string be the document’s fragment directive.
If the document’s allowTextFragmentDirective flag is true then:
Let ranges be a list that is the result of running the process a fragment directive steps with fragment directive string and the document.
If ranges is non-empty, then:
Let range be the first item of ranges.
Let node be the first common ancestor of range’s start node and end node.
While node is non-null and is not an element, set node to node’s parent.
The indicated part of the document is node and range; return.
-
Let commonAncestor be nodeA.
-
While commonAncestor is non-null and is not a shadow-including inclusive ancestor of nodeB, let commonAncestor be commonAncestor’s shadow-including parent.
-
Return commonAncestor.
-
If node is a shadow root, return node’s host.
-
Otherwise, return node’s parent.
3.5.1. Scroll a DOMRect into view
Move the scroll an element into view algorithm’s steps
3-14 into a new algorithm scroll a DOMRect into view, with input DOMRect
bounding box, ScrollIntoViewOptions
dictionary options, and element startingElement.
Also move the recursive behavior described at the top of the scroll an element into view algorithm to the scroll a DOMRect into view algorithm: "run these steps for each ancestor element or viewport of startingElement that establishes a scrolling box scrolling box, in order of innermost to outermost scrolling box".
Monkeypatching [CSSOM-VIEW]:
To scroll a DOMRect into view given a
DOMRect
bounding box, a scroll behavior behavior, a block flow direction position block, and an inline base direction position inline, and element startingElement, means to run these steps for each ancestor element or viewport of startingElement that establishes a scrolling box scrolling box, in order of innermost to outermost scrolling box:OMITTED
TODO: There’s more to do here since the bounding box needs to be transformed with each step to an ancestor element or viewport.
Replace steps 3-14 of the scroll an element into view algorithm with a call to scroll a DOMRect into view:
Monkeypatching [CSSOM-VIEW]:
To scroll an element into view element, with a scroll behavior behavior, a block flow direction position block, and an inline base direction position inline, means to run these steps:
If the
Document
associated with element is not same origin with theDocument
associated with the element or viewport associated with box, terminate these steps.Let element bounding border box be the box that the return value of invoking
getBoundingClientRect()
on element represents.Perform scroll a DOMRect into view given element bounding border box, options and element.
Define a new algorithm for scrolling Range into view:
Monkeypatching [CSSOM-VIEW]:
To scroll a Range into view, with input range range, scroll behavior behavior, a block flow direction position block, an inline base direction position inline, and an element containingElement:
Let bounding rect be the
DOMRect
that is the return value of invokinggetBoundingClientRect()
on range.Perform scroll a DOMRect into view given bounding rect, behavior, block, inline, and containingElement.
3.5.2. Finding Ranges in a Document
At a high level, we take a fragment directive string that looks like this:
text=prefix-,foo&unknown&text=bar,baz
We break this up into the individual text directives:
text=prefix-,foo text=bar,baz
For each text directive, we perform a search in the document for the first instance of rendered text that matches the restrictions in the directive. Each search is independent of any others; that is, the result is the same regardless of how many other directives are provided or their match result.
If a directive successfully matches to text in the document, it returns a range indicating that match in the document. The process a fragment directive steps are the high level API provided by this section. These return a list of ranges that were matched by the individual directive matching steps, in the order the directives were specified in the fragment directive string.
If a directive was not matched, it does not add an item to the returned list.
-
If fragment directive input is not a valid fragment directive, then return an empty list.
-
Let directives be a list of ASCII strings that is the result of strictly splitting the string fragment directive input on "&".
-
For each ASCII string directive of directives:
-
If directive does not match the production TextDirective, then continue.
-
Let parsedValues be the result of running the parse a text directive steps on directive.
-
If parsedValues is null then continue.
-
If the result of running find a range from a text directive given parsedValues and document is non-null, then append it to ranges.
-
-
Return ranges.
textEnd may be null. If omitted, this is an "exact" search and the returned range must contain a string exactly matching textStart. If textEnd is provided, this is a "range" search; the returned range must start with textStart and end with textEnd. In the normative text below, we’ll call a text passage that matches the provided textStart and textEnd, regardless of which mode we’re in, the "matching text".
Either or both of prefix and suffix may be null, in which case context on that side of a match is not checked. E.g. If prefix is null, text is matched without any requirement on what text precedes it.
:~:text=The quick,lazy dogwill fail to match in
<div>The<div> </div>quick brown fox</div> <div>jumped over the lazy dog</div>
because the starting string "The quick" does not appear within a single, uninterrupted block. The instance of "The quick" in the document has a block element between "The" and "quick".
It does, however, match in this example:
<div>The quick brown fox</div> <div>jumped over the lazy dog</div>
-
Let searchRange be a range with start (document, 0) and end (document, document’s length)
-
While searchRange is not collapsed:
-
Let potentialMatch be null.
-
If parsedValues’s prefix is not null:
-
Let prefixMatch be the the result of running the find a string in range steps with query parsedValues’s prefix, searchRange searchRange, wordStartBounded true and wordEndBounded false.
-
If prefixMatch is null, return null.
-
Set searchRange’s start to the first boundary point after prefixMatch’s start
-
Let matchRange be a range whose start is prefixMatch’s end and end is searchRange’s end.
-
Advance matchRange’s start to the next non-whitespace position.
-
If matchRange is collapsed return null.
This can happen if prefixMatch’s end or its subsequent non-whitespace position is at the end of the document. -
Assert: matchRange’s start node is a
Text
node.matchRange’s start now points to the next non-whitespace text data following a matched prefix. -
Let mustEndAtWordBoundary be true if parsedValues’s textEnd is non-null or parsedValues’s suffix is null, false otherwise.
-
Set potentialMatch to the result of running the find a string in range steps with query parsedValues’s textStart, searchRange matchRange, wordStartBounded false, and wordEndBounded mustEndAtWordBoundary.
-
If potentialMatch is null, return null.
-
If potentialMatch’s start is not matchRange’s start, then continue.
In this case, we found a prefix but it was followed by something other than a matching text so we’ll continue searching for the next instance of prefix.
-
-
Otherwise:
-
Let mustEndAtWordBoundary be true if parsedValues’s textEnd is non-null or parsedValues’s suffix is null, false otherwise.
-
Set potentialMatch to the result of running the find a string in range steps with query parsedValues’s textStart, searchRange searchRange, wordStartBounded true, and wordEndBounded mustEndAtWordBoundary.
-
If potentialMatch is null, return null.
-
Set searchRange’s start to the first boundary point after potentialMatch’s start
-
-
If parsedValues’s textEnd item is non-null, then:
-
Let textEndRange be a range whose start is potentialMatch’s end and whose end is searchRange’s end.
-
Let mustEndAtWordBoundary be true if parsedValues’s suffix is null, false otherwise.
-
Let textEndMatch be the result of running the find a string in range steps with query parsedValues’s textEnd, searchRange textEndRange, wordStartBounded true, and wordEndBounded mustEndAtWordBoundary.
-
If textEndMatch is null then return null.
-
-
Assert: potentialMatch is non-null, not collapsed and represents a range exactly containing an instance of matching text.
-
If parsedValues’s suffix is null, return potentialMatch.
-
Let suffixRange be a range with start equal to potentialMatch’s end and end equal to searchRange’s end.
-
Advance suffixRange’s start to the next non-whitespace position.
-
Let suffixMatch be result of running the find a string in range steps with query parsedValues’s suffix, searchRange suffixRange, wordStartBounded false, and wordEndBounded true.
-
If suffixMatch is null then return null.
If the suffix doesn’t appear in the remaining text of the document, there’s no possible way to make a match. -
If suffixMatch’s start is suffixRange’s start, return potentialMatch.
-
-
Return null
-
While range is not collapsed:
-
Let node be range’s start node.
-
Let offset be range’s start offset.
-
If node is part of a non-searchable subtree then:
-
Set range’s start node to the next node, in shadow-including tree order, that isn’t a shadow-including descendant of node, and set its start offset to 0.
-
-
If node is not a visible text node:
-
Set range’s start node to the next node, in shadow-including tree order, and set its start offset to 0.
-
-
If the substring data of node at offset offset and count 6 is equal to the string " " then:
-
Add 6 to range’s start offset.
-
-
Otherwise, if the substring data of node at offset offset and count 5 is equal to the string " " then:
-
Add 5 to range’s start offset.
-
-
Otherwise:
-
Let cp be the code point at the offset index in node’s data.
-
If cp does not have the White_Space property set, return.
-
Add 1 to range’s start offset.
-
-
If range’s start offset is equal to node’s length, set range’s start node to the next node in shadow-including tree order, and set its start offset to 0.
-
The basic premise of this algorithm is to walk all searchable text nodes within a block, collecting them into a list. The list is then concatenated into a single string in which we can search, using the node list to determine offsets with a node so we can return a range.
Collection breaks when we hit a block node, e.g. searching over this tree:
<div> a<em>b</em>c<div>d</div>e </div>
Will perform a search on "abc", then on "d", then on "e".
Thus, query will only match text that is continuous (i.e. uninterrupted by a block-level container) within a single block-level container.
-
While searchRange is not collapsed:
-
Let curNode be searchRange’s start node.
-
If curNode is part of a non-searchable subtree:
-
Set searchRange’s start node to the next node, in shadow-including tree order, that isn’t a shadow-including descendant of curNode.
-
-
If curNode is not a visible text node:
-
Set searchRange’s start node to the next node, in shadow-including tree order, that is not a doctype, and set its start offset to 0.
-
-
Let blockAncestor be the nearest block ancestor of curNode.
-
While curNode is a shadow-including descendant of blockAncestor and the position of the boundary point (curNode, 0) is not after searchRange’s end:
-
If curNode has block-level display then break.
-
If curNode is search invisible:
-
Set curNode to the next node, in shadow-including tree order, that isn’t a shadow-including descendant of curNode.
-
-
If curNode is a visible text node then append it to textNodeList.
-
Set curNode to the next node in shadow-including tree order.
-
-
Run the find a range from a node list steps given query, searchRange, textNodeList, wordStartBounded and wordEndBounded as input. If the resulting range is not null, then return it.
-
If curNode is null, then break.
-
Assert: curNode follows searchRange’s start node.
-
Set searchRange’s start to the boundary point (curNode, 0).
-
-
Return null.
A node is search invisible if it is an element in the HTML namespace and meets any of the following conditions:
-
The computed value of its display property is none.
-
If the node serializes as void.
-
Is any of the following types:
HTMLIFrameElement
,HTMLImageElement
,HTMLMeterElement
,HTMLObjectElement
,HTMLProgressElement
,HTMLStyleElement
,HTMLScriptElement
,HTMLVideoElement
,HTMLAudioElement
-
Is a
select
element whosemultiple
content attribute is absent.
A node is part of a non-searchable subtree if it is or has a shadow-including ancestor that is search invisible.
A node is a visible text node if it is a Text
node, the computed value of its parent element's visibility property is visible, and it is being rendered.
A node has block-level display if it is an element and the computed value of its display property is any of block, table, flow-root, grid, flex, list-item.
-
Let curNode be node.
-
While curNode is non-null
-
If curNode is not a
Text
node and it has block-level display then return curNode. -
Otherwise, set curNode to curNode’s parent.
-
-
Return node’s node document's document element.
Text
nodes nodes, and booleans wordStartBounded and wordEndBounded, follow these steps:
-
When requiring a word boundary at the beginning, it will not match in “color orange”.
-
When requiring a word boundary at the end, it will not match in “forest ranger”.
See § 3.5.3 Word Boundaries for details and more examples.
-
Let searchBuffer be the concatenation of the data of each item in nodes.
data is not correct here since that’s the text data as it exists in the DOM. This algorithm means to run over the text as rendered (and then convert back to Ranges in the DOM). <https://github.com/WICG/scroll-to-text-fragment/issues/98>
-
Let searchStart be 0.
-
If the first item in nodes is searchRange’s start node then set searchStart to searchRange’s start offset.
-
Let start and end be boundary points, initially null.
-
Let matchIndex be null.
-
While matchIndex is null
-
Set matchIndex to the index of the first instance of queryString in searchBuffer, starting at searchStart. The string search must be performed using a base character comparison, or the primary level, as defined in [UTS10].
Intuitively, this is a case-insensitive search also ignoring accents and other marks. -
If matchIndex is null, return null.
-
Let endIx be matchIndex + queryString’s length.
endIx is the index of the last character in the match + 1. -
Set start to the boundary point result of get boundary point at index matchIndex run over nodes with isEnd false.
-
Set end to the boundary point result of get boundary point at index endIx run over nodes with isEnd true.
-
If wordStartBounded is true and matchIndex is not at a word boundary in searchBuffer, given the language from start’s node as the locale; or wordEndBounded is true and matchIndex + queryString’s length is not at a word boundary in searchBuffer, given the language from end’s node as the locale:
-
Set searchStart to matchIndex + 1.
-
Set matchIndex to null.
-
-
-
Let endInset be 0.
-
If the last item in nodes is searchRange’s end node then set endInset to (searchRange’s end node's length − searchRange’s end offset)
endInset is the offset from the last position in the last node in the reverse direction. Alternatively, it is the length of the node that’s not included in the range. -
If matchIndex + queryString’s length is greater than searchBuffer’s length − endInset return null.
If the match runs past the end of the search range, return null. -
Assert: start and end are non-null, valid boundary points in searchRange.
Text
nodes nodes, and a boolean isEnd, follow these steps:
This is a small helper routine used by the steps above to determine which node a given index in the concatenated string belongs to.
isEnd is used to differentiate start and end indices. An end index points to the "one-past-last" character of the matching string. If the match ends at node boundary, we want the end offset to remain within that node, rather than the start of the next node.
-
Let counted be 0.
-
For each curNode of nodes:
-
Let nodeEnd be counted + curNode’s length.
-
If isEnd is true, add 1 to nodeEnd.
-
If nodeEnd is greater than index then:
-
Return the boundary point (curNode, index − counted).
-
-
Increment counted by curNode’s length.
-
-
Return null.
3.5.3. Word Boundaries
A word boundary is defined in [UAX29] in Unicode Text Segmentation §Word_Boundaries. Unicode Text Segmentation §Default_Word_Boundaries defines a default set of what constitutes a word boundary, but as the specification mentions, a more sophisticated algorithm should be used based on the locale.
Dictionary-based word bounding should take specific care in locales without a word-separating character. E.g. In English, words are separated by the space character (' '); however, in Japanese there is no character that separates one word from the next. In such cases, and where the alphabet contains fewer than 100 characters, the dictionary must not contain more than 20% of the alphabet as valid, one-letter words.
A locale is a string containing a valid [BCP47] language tag, or the empty string. An empty string indicates that the primary language is unknown.
A substring is word bounded in a string text, given locales startLocale and endLocale, if both the position of its first character is at a word boundary given startLocale, and the position after its last character is at a word boundary given endLocale.
A number position is at a word boundary in a string text, given a locale locale, if, using locale, either a word boundary immediately precedes the positionth code unit, or text’s length is more than 0 and position equals either 0 or text’s length.
In languages with a word separator (e.g. " " space) this is (mostly) straightforward; though there are details covered by the above technical reports such as new lines, hyphenations, quotes, etc.
Some languages do not have such a separator (notably, Chinese/Japanese/Korean). Languages such as these requires dictionaries to determine what a valid word in the given locale is.
Text fragments are restricted such that match terms, when combined with
their adjacent context terms, must be word bounded. For example, in an
exact search like prefix,textStart,suffix
, "prefix+textStart+suffix"
must be word bounded. However, in a
range search like prefix,textStart,textEnd,suffix
, both "prefix+textStart"
and "textEnd+suffix"
must be
word bounded.
The goal is that a third-party must already know the full tokens they are
matching against. A range match like textStart,textEnd
must be
word bounded on the inside of the two terms; otherwise a third party could
use this repeatedly to try and reveal a token (e.g. on a page with "Balance: 123,456 $"
, a third-party could set prefix="Balance: ", textEnd="$"
and vary textStart
to try and guess the numeric token one digit at a time).
For more details, refer to the Security Review Doc
3.6. Indicating The Text Match
The UA may choose to scroll the text fragment into view as part of the try to scroll to the fragment steps or by some other mechanism; however, it is not required to scroll the match into view.
The UA should visually indicate the matched text in some way such that the user is made aware of the text match, such as with a high-contrast highlight.
The UA should provide to the user some method of dismissing the match, such that the matched text no longer appears visually indicated.
The exact appearance and mechanics of the indication are left as UA-defined. However, the UA must not use the Document’s selection to indicate the text match as doing so could allow attack vectors for content exfiltration.
The UA must not visually indicate any provided context terms.
Since the indicator is not part of the document’s content, UAs should consider ways to differentiate it from the page’s content as perceived by the user.
3.6.1. URLs in UA features
UAs provide a number of consumers for a document’s URL (outside of programmatic
APIs like window.location
). Examples include a location bar
indicating the URL of the currently visible document, or the URL used when a
user requests to create a bookmark for the current page.
To avoid user confusion, UAs should be consistent in whether such URLs include the fragment directive. This section provides a default set of recommendations for how UAs should handle these cases.
We provide these as a baseline for consistent behavior; however, as these features don’t affect cross-UA interoperability, they are not strict conformance requirements.
Exact behavior is left up to the implementing UA which may have differing constraints or reasons for modifying the behavior. e.g. UAs may allow users to configure defaults or expose UI options so users can choose whether they prefer to include fragment directives in these URLs.
It’s also useful to allow UAs to experiment with providing a better experience. E.g. perhaps a URL should elide the text fragment if the user scrolls it out of view?
The general principle is that a URL should include the fragment directive only while the visual indicator is visible (i.e. not dismissed). If the user dismisses the indicator, the URL should not include the fragment directive.
If the URL includes a text fragment but a match wasn’t found in the current page, the UA may choose to omit it from the exposed URL.
A text fragment that isn’t found on the page may be useful information to surface to a user to indicate that the page may have changed since the link was created.
However, it’s unlikely to be useful to the user in a bookmark.
A few common examples are provided below.
3.6.1.1. Location Bar
The location bar’s URL should include a text fragment while it is visually indicated. The fragment directive should be stripped from the location bar URL when the user dismisses the indication.
It is recommended that the text fragment be displayed in the location bar’s URL even if a match wasn’t located in the document.
3.6.1.2. Bookmarks
Many UAs provide a "bookmark" feature allowing users to store a convenient link to the current page in the UA’s interface.
A newly created bookmark should, by default, include the fragment directive in the URL if, and only if, a match was found and the visual indicator hasn’t been dismissed.
Navigating to a URL from a bookmark should process a fragment directive as if it were navigated to in a typical navigation.
3.6.1.3. Sharing
Some UAs provide a method for users to share the current page with others, typically by providing the URL to another app or messaging service.
When providing a URL in these situations, it should include the fragment directive if, and only if, a match was found and the visual indicator hasn’t been dismissed.
3.7. Document Policy Integration
This specification defines a configuration point in Document Policy with name "force-load-at-top". Its type is boolean
with default value false
.
https://example.com#:~:text=foo
. The
example.com server response includes the header:
Document-Policy: force-load-at-top
When the page loads, the element containing "foo" will be marked as the indicated part of the document and set as the document’s target element. However, "foo" will not be scrolled into view.
Fragment-based scroll blocking from this policy is specified in an amendment to the scroll to the fragment algorithm in the § 3.5 Navigating to a Text Fragment section of this document.
History scroll restoration is blocked by amending the restore persisted state steps by inserting a new step after 2:
-
Get the document policy value of the "force-load-at-top" feature for the Document. If the result is true, then the user agent should not restore the scroll position for the Document or any of its scrollable regions. Scroll positions for child browsing contexts should be restored based on the value of this policy in the child Document.
3.8. Feature Detectability
For feature detectability, we propose adding a new FragmentDirective interface
that is exposed via document.fragmentDirective
if the UA supports
the feature.
[Exposed =Window ]interface { };
FragmentDirective
We amend the Document
interface to include a fragmentDirective
property:
partial interface Document { [SameObject ]readonly attribute FragmentDirective ; };
fragmentDirective
This object may be used to expose additional information about the text fragment or other fragment directives in the future.
4. Generating Text Fragment Directives
This section contains recommendations for UAs automatically generating URLs with a text fragment directive. These recommendations aren’t normative but are provided to ensure generated URLs result in maximally stable and usable URLs.
4.1. Prefer Exact Matching To Range-based
The match text can be provided either as an exact string "text=foo%20bar%20baz" or as a range "text=foo,bar".
UAs should prefer to specify the entire string where practical. This ensures that if the destination page is removed or changed, the intended destination can still be derived from the URL itself.
The first recorded idea of using digital electronics for computing was the 1931 paper "The Use of Thyratrons for High Speed Automatic Counting of Physical Phenomena" by C. E. Wynn-Williams.
We could create a range-based match like so:
https://en.wikipedia.org/wiki/History_of_computing#:~:text=The%20first%20recorded,Williams
Or we could encode the entire sentence using an exact match term:
The range-based match is less stable, meaning that if the page is changed to include another instance of "The first recorded" somewhere earlier in the page, the link will now target an unintended text snippet.
The range-based match is also less useful semantically. If the page is changed to remove the sentence, the user won’t know what the intended target was. In the exact match case, the user can read, or the UA can surface, the text that was being searched for but not found.
Range-based matches can be helpful when the quoted text is excessively long and encoding the entire string would produce an unwieldy URL.
It is recommended that text snippets shorter than 300 characters always be encoded using an exact match. Above this limit, the UA should encode the string as a range-based match.
4.2. Use Context Only When Necessary
Context terms allow the text fragment directive to disambiguate text snippets on a page. However, their use can make the URL more brittle in some cases. Often, the desired string will start or end at an element boundary. The context will therefore exist in an adjacent element. Changes to the page structure could invalidate the text fragment directive since the context and match text may no longer appear to be adjacent.
<div class="section">HEADER</div> <div class="content">Text to quote</div>
We could craft the text fragment directive as follows:
text=HEADER-,Text%20to%20quote
However, suppose the page changes to add a "[edit]" link beside all section headers. This would now break the URL.
Where a text snippet is long enough and unique, a UA should prefer to avoid adding superfluous context terms.
It is recommended that context should be used only if one of the following is true:
- The UA determines the quoted text is ambiguous
- The quoted text contains 3 or fewer words
4.3. Determine If Fragment Id Is Needed
When the UA navigates to a URL containing a text fragment directive, it will fallback to scrolling into view a regular element-id based fragment if it exists and the text fragment isn’t found.
This can be useful to provide a fallback, in case the text in the document changes, invalidating the text fragment directive.
The earliest known tool for use in computation is the Sumerian abacus
By specifying the section that the text appears in, we ensure that, if the text is changed or removed, the user will still be pointed to the relevant section:
However, UAs should take care that the fallback element-id fragment is the correct one:
By the late 1960s, computer systems could perform symbolic algebraic manipulations
The UA should note that, even though the current URL of the page is: https://en.wikipedia.org/wiki/History_of_computing#Early_computation, using #Early_computation as a fallback is inappropriate. If the above sentence is changed or removed, the page will load in the #Early_computation section which could be quite confusing to the user.
If the UA cannot reliably determine an appropriate fragment to fallback to, it should remove the fragment id from the URL:
If a UA chooses not to scroll text fragments into view on navigation (reasons why a UA may make this choice are discussed in § 3.4 Security and Privacy), it must scroll the element-id into view, if provided, regardless of whether a text fragment was matched. Not doing so would allow detecting the text fragment match based on whether the element-id was scrolled.