Writing Assistance APIs

1. Introduction

For now, see the explainer.

2. Shared APIs

partial interface WindowOrWorkerGlobalScope {
  [Replaceable, SecureContext] readonly attribute AI ai;
};

[Exposed=(Window,Worker), SecureContext]
interface AI {};

[Exposed=(Window,Worker), SecureContext]
interface AICreateMonitor : EventTarget {
  attribute EventHandler ondownloadprogress;
};

callback AICreateMonitorCallback = undefined (AICreateMonitor monitor);

enum AIAvailability {
  "unavailable",
  "downloadable",
  "downloading",
  "available"
};

interface mixin AIDestroyable {
  undefined destroy();
};

Every WindowOrWorkerGlobalScope has an AI namespace, an AI object. Upon creation of the WindowOrWorkerGlobalScope object, its AI namespace must be set to a new AI object created in the WindowOrWorkerGlobalScope object’s relevant realm.

The ai getter steps are to return this’s AI namespace.

The following are the event handlers (and their corresponding event handler event types) that must be supported, as event handler IDL attributes, by all AICreateMonitor objects:

Event handler	Event handler event type
`ondownloadprogress`	`downloadprogress`

Every interface including the AIDestroyable interface mixin has a destruction abort controller, an AbortController, set by the initialize as a destroyable algorithm.

The destruction abort controller is only used internally, as a way of tracking calls to destroy(). Since it is easy to combine multiple AbortSignals using create a dependent abort signal, this lets us centralize handling of any AbortSignal the web developer provides to specific method calls, with any calls to destroy().

To initialize as a destroyable an AIDestroyable object destroyable:

Let controller be a new AbortController created in destroyable’s relevant realm.
Set controller’s signal to a new AbortSignal created in destroyable’s relevant realm.
Set destroyable’s destruction abort controller to controller.

The destroy() method steps are to destroy this given a new "AbortError" DOMException.

To destroy an AIDestroyable destroyable, given a JavaScript value reason:

Signal abort given destroyable’s destruction abort controller and reason.
The user agent should release any resources associated with destroyable, such as AI models loaded to support its operation, as long as those resources are not needed for other ongoing operations.

3. The summarizer API

partial interface AI {
  readonly attribute AISummarizerFactory summarizer;
};

[Exposed=(Window,Worker), SecureContext]
interface AISummarizerFactory {
  Promise<AISummarizer> create(optional AISummarizerCreateOptions options = {});
  Promise<AIAvailability> availability(optional AISummarizerCreateCoreOptions options = {});
};

[Exposed=(Window,Worker), SecureContext]
interface AISummarizer {
  Promise<DOMString> summarize(
    DOMString input,
    optional AISummarizerSummarizeOptions options = {}
  );
  ReadableStream summarizeStreaming(
    DOMString input,
    optional AISummarizerSummarizeOptions options = {}
  );

  readonly attribute DOMString sharedContext;
  readonly attribute AISummarizerType type;
  readonly attribute AISummarizerFormat format;
  readonly attribute AISummarizerLength length;

  readonly attribute FrozenArray<DOMString>? expectedInputLanguages;
  readonly attribute FrozenArray<DOMString>? expectedContextLanguages;
  readonly attribute DOMString? outputLanguage;
};
AISummarizer includes AIDestroyable;

dictionary AISummarizerCreateCoreOptions {
  AISummarizerType type = "key-points";
  AISummarizerFormat format = "markdown";
  AISummarizerLength length = "short";

  sequence<DOMString> expectedInputLanguages;
  sequence<DOMString> expectedContextLanguages;
  DOMString outputLanguage;
};

dictionary AISummarizerCreateOptions : AISummarizerCreateCoreOptions {
  AbortSignal signal;
  AICreateMonitorCallback monitor;

  DOMString sharedContext;
};

dictionary AISummarizerSummarizeOptions {
  AbortSignal signal;
  DOMString context;
};

enum AISummarizerType { "tl;dr", "teaser", "key-points", "headline" };
enum AISummarizerFormat { "plain-text", "markdown" };
enum AISummarizerLength { "short", "medium", "long" };

Every AI has an summarizer factory, an AISummarizerFactory object. Upon creation of the AI object, its summarizer factory must be set to a new AISummarizerFactory object created in the AI object’s relevant realm.

The summarizer getter steps are to return this’s summarizer factory.

3.1. Creation

The create(options) method steps are:

If this’s relevant global object is a Window whose associated Document is not fully active, then return a promise rejected with an "InvalidStateError" DOMException.
If options["signal"] exists and is aborted, then return a promise rejected with options["signal"]'s abort reason.
Validate and canonicalize summarizer options given options. If this throws an exception e, catch it, and return a promise rejected with e.

This can mutate options.
Return the result of creating an AI model object given this’s relevant realm, options, computing summarizer options availability, download the summarization model, initialize the summarization model, and create a summarizer object.

To validate and canonicalize summarizer options given an AISummarizerCreateCoreOptions options, perform the following steps. They mutate options in place to canonicalize and deduplicate language tags, and throw a TypeError if any are invalid.

Validate and canonicalize language tags given options and "expectedInputLanguages".
Validate and canonicalize language tags given options and "expectedContextLanguages".
Validate and canonicalize language tags given options and "outputLanguage".

To download the summarization model, given an AISummarizerCreateCoreOptions options:

Assert: these steps are running in parallel.
Initiate the download process for everything the user agent needs to summarize text according to options. This could include a base AI model, fine-tunings for specific languages or option values, or other resources.
If the download process cannot be started for any reason, then return false.
Return true.

To initialize the summarization model, given an AISummarizerCreateOptions options:

Assert: these steps are running in parallel.
Perform any necessary initialization operations for the AI model backing the user agent’s summarization capabilities.

This could include loading the model into memory, loading options["sharedContext"] into the model’s context window, or loading any fine-tunings necessary to support the other options expressed by options.
If initialization failed for any reason, then return false.
Return true.

To create a summarizer object, given a realm realm and an AISummarizerCreateOptions options:

Assert: these steps are running on realm’s surrounding agent’s event loop.
Return a new AISummarizer object, created in realm, with

shared context

options["sharedContext"] if it exists; otherwise null

summary type

options["type"]

summary format

options["format"]

summary length

options["length"]

expected input languages

the result of creating a frozen array given options["expectedInputLanguages"] if it is not empty; otherwise null

expected context languages

the result of creating a frozen array given options["expectedContextLanguages"] if it is not empty; otherwise null

output language

options["outputLanguage"] if it exists; otherwise null

3.2. Availability

The availability(options) method steps are:

If this’s relevant global object is a Window whose associated Document is not fully active, then return a promise rejected with an "InvalidStateError" DOMException.
Validate and canonicalize summarizer options given options.
Let promise be a new promise created in this’s relevant realm.
In parallel:
1. Let availability be the result of computing summarizer options availability given options.
2. Queue a global task on the AI task source given this’s relevant global object to perform the following steps:
  1. If availability is null, then reject promise with an "UnknownError" DOMException.
  2. Otherwise, resolve promise with availability.

To compute summarizer options availability given an AISummarizerCreateCoreOptions options, perform the following steps. They return either an AIAvailability value or null, and they mutate options in place to update language tags to their best-fit matches.

Assert: this algorithm is running in parallel.
Let availability be the summarizer non-language options availability given options["type"], options["format"], and options["length"].
Let languageAvailabilities be the summarizer language availabilities.
If languageAvailabilities is null, then return null.
Let inputLanguageAvailability be the result of computing summarizer language availability given options["expectedInputLanguages"] and languageAvailabilities’s input languages.
Let contextLanguagesAvailability be the result of computing summarizer language availability given options["expectedContextLanguages"] and languageAvailabilities’s context languages.
Let outputLanguagesList be « options["outputLanguage"] ».
Let outputLanguageAvailability be the result of computing summarizer language availability given outputLanguagesList and languageAvailabilities’s output languages.
Set options["outputLanguage"] to outputLanguagesList[0].
Return the minimum availability given « availability, inputLanguageAvailability, contextLanguagesAvailability, outputLanguageAvailability ».

To compute summarizer language availability given an ordered set of strings requestedLanguages and a map from AIAvailability values to sets of strings availabilities, perform the following steps. They return an AIAvailability value, and they mutate requestedLanguages in place to update language tags to their best-fit matches.

Let availability be "available".
For each language of requestedLanguages:
1. For each availabilityToCheck of « "available", "downloading", "downloadable" »:
  1. Let languagesWithThisAvailability be availabilities[availabilityToCheck].
  2. Let bestMatch be LookupMatchingLocaleByBestFit(languagesWithThisAvailability, « language »).
  3. If bestMatch is not undefined, then:
    1. Replace language with bestMatch.[[locale]] in requestedLanguages.
    2. Set availability to the minimum availability given availability and availabilityToCheck.
    3. Break.
2. Return "unavailable".
Return availability.

The summarizer non-language options availability, given a AISummarizerType type, AISummarizerFormat format, and an AISummarizerLength length, is given by the following steps. They return an AIAvailability value or null.

Assert: this algorithm is running in parallel.
If there is some error attempting to determine whether the user agent supports summarizing text, which the user agent believes to be transient (such that re-querying the summarizer non-language options availability could stop producing such an error), then return null.
If the user agent supports summarizing text into the type of summary described by type, in the format described by format, and with the length guidance given by length without performing any downloading operations, then return "available".
If the user agent believes it can summarize text according to type, format, and length, but only after finishing a download (e.g., of an AI model or fine-tuning) that is already ongoing, then return "downloadable".
If the user agent believes it can summarize text according to type, format, and length, but only after performing a download (e.g., of an AI model or fine-tuning), then return "downloadable".
Otherwise, return "unavailable".

A language availabilities is a struct with the following items:

input languages
context languages
output languages

All of these items are maps from AIAvailability values to sets of strings representing Unicode canonicalized locale identifiers. Their keys will always be one of "downloading", "downloadable", or "available" (i.e., they will never be "unavailable"). [ECMA-402]

The summarizer language availabilities are given by the following steps. They return a language availabilities or null.

Assert: this algorithm is running in parallel.
If there is some error attempting to determine whether the user agent supports summarizing text, which the user agent believes to be transient (such that re-querying the summarizer language availabilities could stop producing such an error), then return null.
Return a language availabilities with:

input languages

the result of getting language availabilities given the purpose of summarizing text written in that language

context languages

the result of getting language availabilities given the purpose of summarizing text using web-developer provided context information written in that language

output languages

the result of getting language availabilities given the purpose of producing text summaries in that language

A common setup seen in today’s software is to support two types of written Chinese: "traditional Chinese" and "simplified Chinese". Let’s suppose that the user agent supports summarizing text written in traditional Chinese with no downloads, and simplified Chinese after a download.

One way this could be implemented would be for summarizer language availabilities to return that "zh-Hant" is in the input languages["available"] set, and "zh" and "zh-Hans" are in the input languages["downloadable"] set. This return value conforms to the requirements of the language tag set completeness rules, in ensuring that "zh" is present. Per the "should"-level guidance, the implementation has determined that "zh" belongs in the set of downloadable input languages, with "zh-Hans", instead of in the set of available input languages, with "zh-Hant".

Combined with the use of LookupMatchingLocaleByBestFit, this means availability() will give the following answers:

function a(languageTag) {
  return ai.summarizer.availability({
    expectedInputLanguages: [languageTag]
  });
}

await a("zh") === "downloadable";
await a("zh-Hant") === "available";
await a("zh-Hans") === "downloadable";

await a("zh-TW") === "available";      // zh-TW will best-fit to zh-Hant
await a("zh-HK") === "available";      // zh-HK will best-fit to zh-Hant
await a("zh-CN") === "downloadable";   // zh-CN will best-fit to zh-Hans

await a("zh-BR") === "downloadable";   // zh-BR will best-fit to zh
await a("zh-Kana") === "downloadable"; // zh-Kana will best-fit to zh

3.3. The `AISummarizer` class

Every AISummarizer has a shared context, a string-or-null, set during creation.

Every AISummarizer has a summary type, an AISummarizerType, set during creation.

Every AISummarizer has a summary format, an AISummarizerFormat, set during creation.

Every AISummarizer has a summary length, an AISummarizerLength, set during creation.

Every AISummarizer has an expected input languages, a FrozenArray<DOMString> or null, set during creation.

Every AISummarizer has an expected context languages, a FrozenArray<DOMString> or null, set during creation.

Every AISummarizer has an output language, a string or null, set during creation.

The sharedContext getter steps are to return this’s shared context.

The type getter steps are to return this’s summary type.

The format getter steps are to return this’s summary format.

The length getter steps are to return this’s summary length.

The expectedInputLanguages getter steps are to return this’s expected input languages.

The expectedContextLanguages getter steps are to return this’s expected context languages.

The outputLanguage getter steps are to return this’s output language.

The summarize(input, options) method steps are:

Let context be options["context"] if it exists; otherwise null.
Let operation be an algorithm step which takes arguments chunkProduced, done, error, and stopProducing, and summarizes input given this’s shared context, context, this’s summary type, this’s summary format, this’s summary length, this’s output language, chunkProduced, done, error, and stopProducing.
Return the result of getting an aggregated AI model result given this, options, and operation.

The summarizeStreaming(input, options) method steps are:

Let context be options["context"] if it exists; otherwise null.
Let operation be an algorithm step which takes arguments chunkProduced, done, error, and stopProducing, and summarizes input given this’s shared context, context, this’s summary type, this’s summary format, this’s summary length, this’s output language, chunkProduced, done, error, and stopProducing.
Return the result of getting a streaming AI model result given this, options, and operation.

3.4. Summarization

3.4.1. The algorithm

To summarize given:

a string input,
a string-or-null sharedContext,
a string-or-null context,
an AISummarizerType type,
an AISummarizerFormat format,
an AISummarizerLength length,
a string-or-null outputLanguage,
an algorithm chunkProduced that takes a string and returns nothing,
an algorithm done that takes no arguments and returns nothing,
an algorithm error that takes error information and returns nothing, and
an algorithm stopProducing that takes no arguments and returns a boolean,

perform the following steps:

Assert: this algorithm is running in parallel.
In an implementation-defined manner, subject to the following guidelines, begin the processs of summarizing input into a string.

If they are non-null, sharedContext and context should be used to aid in the summarization by providing context on how the web developer wishes the input to be summarized.

If input is the empty string, or otherwise consists of no summarizable content (e.g., only contains whitespace, or control characters), then the resulting summary should be the empty string. In such cases, sharedContext, context, type, format, length, and outputLanguage should be ignored.

The summarization should conform to the guidance given by type, format, and length, in the definitions of each of their enumeration values.

If outputLanguage is non-null, the summarization should be in that language. Otherwise, it should be in the language of input (which might not match that of context or sharedContext). If input contains multiple languages, or the language of input cannot be detected, then either the output language is implementation-defined, or the implementation may treat this as an error, per the guidance in § 3.4.3 Errors.
While true:
1. Wait for the next chunk of summarization data to be produced, for the summarization process to finish, or for the result of calling stopProducing to become true.
2. If such a chunk is successfully produced:
  1. Let it be represented as a string chunk.
  2. Perform chunkProduced given chunk.
3. Otherwise, if the summarization process has finished:
  1. Perform done.
  2. Break.
4. Otherwise, if stopProducing returns true, then break.
5. Otherwise, if an error occurred during summarization:
  1. Let the error be represented as error information errorInfo according to the guidance in § 3.4.3 Errors.
  2. Perform error given errorInfo.
  3. Break.

3.4.2. Options

The summarize algorithm’s details are implementation-defined, as they are expected to be powered by an AI model. However, it is intended to be controllable by the web developer through the AISummarizerType, AISummarizerFormat, and AISummarizerLength enumerations.

This section gives normative guidance on how the implementation of summarize should use each enumeration value to guide the summarization process.

`AISummarizerType` values
Value	Meaning
"`tl;dr`"	The summary should be short and to the point, providing a quick overview of the input, suitable for a busy reader.
"`teaser`"	The summary should focus on the most interesting or intriguing parts of the input, designed to draw the reader in to read more.
"`key-points`"	The summary should extract the most important points from the input, presented as a bulleted list.
"`headline`"	The summary should effectively contain the main point of the input in a single sentence, in the format of an article headline.

`AISummarizerLength` values
Value	Meaning
"`short`"	The guidance is dependent on the value of `AISummarizerType`: "`tl;dr`" "`teaser`" The summary should fit within 1 sentence. "`key-points`" The summary should consist of no more than 3 bullet points. "`headline`" The summary should use no more than 12 words.
"`medium`"	The guidance is dependent on the value of `AISummarizerType`: "`tl;dr`" "`teaser`" The summary should fit within 1 short paragraph. "`key-points`" The summary should consist of no more than 5 bullet points. "`headline`" The summary should use no more than 17 words.
"`long`"	The guidance is dependent on the value of `AISummarizerType`: "`tl;dr`" "`teaser`" The summary should fit within 1 paragraph. "`key-points`" The summary should consist of no more than 7 bullet points. "`headline`" The summary should use no more than 22 words.

As with all "should"-level guidance, user agents might not conform perfectly to these. Especially in the case of counting words, it’s expected that language models might not conform perfectly.

`AISummarizerFormat` values
Value	Meaning
"`plain-text`"	The summary should not contain any formatting or markup language.
"`markdown`"	The summary should be formatted using the Markdown markup language, ideally as valid CommonMark. [COMMONMARK]

3.4.3. Errors

When summarization fails, the following possible reasons may be surfaced to the web developer. This table lists the possible DOMException names and the cases in which an implementation should use them:

`DOMException` name	Scenarios
"`NotAllowedError`"	Summarization is disabled by user choice or user agent policy.
"`NotReadableError`"	The summarization output was filtered by the user agent, e.g., because it was detected to be harmful, inaccurate, or nonsensical.
"`NotSupportedError`"	The input to be summarized, or the context to be provided, was in a language that the user agent does not support, or was not provided properly in the call to `create()`. The summarization output ended up being in a language that the user agent does not support (e.g., because the user agent has not performed sufficient quality control tests on that output language), or was not provided properly in the call to `create()`. The `outputLanguage` option was not set, and the language of the input text could not be determined, so the user agent did not have a good output language default available.
"`QuotaExceededError`"	The input to be summarized was too large for the user agent to handle.
"`UnknownError`"	All other scenarios, or if the user agent would prefer not to disclose the failure reason.

This table does not give the complete list of exceptions that can be surfaced by summarizer.summarize() and summarizer.summarizeStreaming(). It only contains those which can come from the implementation-defined summarize algorithm.

4. The writer API

Just IDL for now; full spec coming!

[Exposed=(Window,Worker), SecureContext]
interface AIWriterFactory {
  Promise<AIWriter> create(optional AIWriterCreateOptions options = {});
  Promise<AIAvailability> availability(optional AIWriterCreateCoreOptions options = {});
};

[Exposed=(Window,Worker), SecureContext]
interface AIWriter {
  Promise<DOMString> write(DOMString writingTask, optional AIWriterWriteOptions options = {});
  ReadableStream writeStreaming(DOMString writingTask, optional AIWriterWriteOptions options = {});

  readonly attribute DOMString sharedContext;
  readonly attribute AIWriterTone tone;
  readonly attribute AIWriterFormat format;
  readonly attribute AIWriterLength length;

  readonly attribute FrozenArray<DOMString>? expectedInputLanguages;
  readonly attribute FrozenArray<DOMString>? expectedContextLanguages;
  readonly attribute DOMString? outputLanguage;
};
AIWriter includes AIDestroyable;

dictionary AIWriterCreateCoreOptions {
  AIWriterTone tone = "neutral";
  AIWriterFormat format = "markdown";
  AIWriterLength length = "short";

  sequence<DOMString> expectedInputLanguages;
  sequence<DOMString> expectedContextLanguages;
  DOMString outputLanguage;
};

dictionary AIWriterCreateOptions : AIWriterCreateCoreOptions {
  AbortSignal signal;
  AICreateMonitorCallback monitor;

  DOMString sharedContext;
};

dictionary AIWriterWriteOptions {
  DOMString context;
  AbortSignal signal;
};

enum AIWriterTone { "formal", "neutral", "casual" };
enum AIWriterFormat { "plain-text", "markdown" };
enum AIWriterLength { "short", "medium", "long" };

5. The rewriter API

Just IDL for now; full spec coming!

[Exposed=(Window,Worker), SecureContext]
interface AIRewriterFactory {
  Promise<AIRewriter> create(optional AIRewriterCreateOptions options = {});
  Promise<AIAvailability> availability(optional AIRewriterCreateCoreOptions options = {});
};

[Exposed=(Window,Worker), SecureContext]
interface AIRewriter {
  Promise<DOMString> rewrite(DOMString input, optional AIRewriterRewriteOptions options = {});
  ReadableStream rewriteStreaming(DOMString input, optional AIRewriterRewriteOptions options = {});

  readonly attribute DOMString sharedContext;
  readonly attribute AIRewriterTone tone;
  readonly attribute AIRewriterFormat format;
  readonly attribute AIRewriterLength length;

  readonly attribute FrozenArray<DOMString>? expectedInputLanguages;
  readonly attribute FrozenArray<DOMString>? expectedContextLanguages;
  readonly attribute DOMString? outputLanguage;
};
AIRewriter includes AIDestroyable;

dictionary AIRewriterCreateCoreOptions {
  AIRewriterTone tone = "as-is";
  AIRewriterFormat format = "as-is";
  AIRewriterLength length = "as-is";

  sequence<DOMString> expectedInputLanguages;
  sequence<DOMString> expectedContextLanguages;
  DOMString outputLanguage;
};

dictionary AIRewriterCreateOptions : AIRewriterCreateCoreOptions {
  AbortSignal signal;
  AICreateMonitorCallback monitor;

  DOMString sharedContext;
};

dictionary AIRewriterRewriteOptions {
  DOMString context;
  AbortSignal signal;
};

enum AIRewriterTone { "as-is", "more-formal", "more-casual" };
enum AIRewriterFormat { "as-is", "plain-text", "markdown" };
enum AIRewriterLength { "as-is", "shorter", "longer" };

6. Shared infrastructure

6.1. Creation

To create an AI model object given:

a realm realm,
an ordered map options,
an algorithm getAvailability taking an ordered map and returning an AIAvailability or null,
an algorithm startDownload taking an ordered map and returning a boolean,
an algorithm initialize taking an ordered map and returning a boolean, and
an algorithm create taking a realm and an ordered map and returning a Web IDL object representing the model,

perform the following steps:

Let fireProgressEvent be an algorithm taking two arguments that does nothing.
If options["monitor"] exists, then:
1. Let monitor be a new AICreateMonitor created in realm.
2. Invoke options["monitor"] with « monitor » and "rethrow".
  
  If this throws an exception e, catch it, and return a promise rejected with e.
3. Set fireProgressEvent to an algorithm taking argument loaded, which performs the following steps:
  1. Assert: this algorithm is running in parallel.
  2. Queue a global task on the AI task source given realm’s global object to perform the following steps:
    1. Fire an event named downloadprogress at monitor, using ProgressEvent, with the loaded attribute initialized to loaded, the total attribute initialized to 1, and the lengthComputable attribute initialized to true.
      
      This assumes whatwg/xhr#394 is merged so that passing non-integer values for loaded works as expected.
Let abortedDuringDownload be false.

This variable will be written to from the event loop, but read from in parallel.
If options["signal"] exists, then add the following abort steps to options["signal"]:
1. Set abortedDuringDownload to true.
Let promise be a new promise created in realm.
In parallel:
1. Let availability be the result of performing getAvailability given options.
  
  This can mutate options.
2. Switch on availability:
null
1. Reject promise with an "UnknownError" DOMException.
2. Abort these steps.
"unavailable"
1. Reject promise with a "NotSupportedError" DOMException.
2. Abort these steps.
"available"
1. Initialize and return an AI model object given promise, options, fireProgressEvent, initialize, and create.
"downloading"
"downloadable"
1. If availability is "downloadable", then let startDownloadResult be the result of performing startDownload given options.
2. If startDownloadResult is false, then:
  1. Queue a global task on the AI task source given realm’s global object to reject promise with a "NetworkError" DOMException.
  2. Abort these steps.
3. Run the following steps, but abort when abortedDuringDownload becomes true:
  1. Wait for the total number of bytes to be downloaded to become determined, and let that number be totalBytes.
  2. Let lastProgressTime be the monotonic clock’s unsafe current time.
  3. Perform fireProgressEvent given 0.
  4. While true:
    
    If one or more bytes have been downloaded, then:
    
    If the monotonic clock’s unsafe current time minus lastProgressTime is greater than 50 ms, then:
    
    Let bytesSoFar be the number of bytes downloaded so far.
    
    Assert: bytesSoFar is greater than 0 and less than or equal to totalBytes.
    
    Let rawProgressFraction be bytesSoFar divided by totalBytes.
    
    Let progressFraction be floor(rawProgressFraction × 65,536) ÷ 65,536.
    
    Perform fireProgressEvent given progressFraction.
    
    We use a fraction, instead of firing a progress event with the number of bytes downloaded, to avoid giving precise information about the size of the model or other material being downloaded.
    
    progressFraction is calculated from rawProgressFraction to give a precision of one part in 2¹⁶. This ensures that over most internet speeds and with most model sizes, the loaded value will be different from the previous one that was fired ~50 milliseconds ago.
    
    Full calculation
    
    Assume a 5 GiB download size, and a 20 Mbps download speed (chosen as a number on the lower range from this source). Then, downloading 5 GiB will take:
    $\begin{matrix} 5 GiB \times \frac{2^{30} bytes}{GiB} \times \frac{8 bits}{bytes} \div \frac{20 \times 10^{6} bits}{s} \times \frac{1000 ms}{s} \div \frac{50 ms}{interval} \\ = & 49,950 intervals \end{matrix}$
    Rounding up to the nearest power of two gives a conservative estimate of 65,536 fifty millisecond intervals, so we want to give progress to 1 part in 2¹⁶.
    
    If bytesSoFar equals totalBytes, then break.
    
    Since this is the only exit condition for the loop, we are guaranteed to fire a downloadprogress event for the 100% mark.
    
    Set lastProgressTime to the monotonic clock’s unsafe current time.
    
    Otherwise, if downloading has failed and cannot continue, then:
    
    Queue a global task on the AI task source given realm’s global object to reject promise with a "NetworkError" DOMException.
    
    Abort these steps.
4. If aborted, then:
  1. Queue a global task on the AI task source given realm’s global object to perform the following steps:
    
    Assert: options["signal"] is aborted.
    
    Reject promise with options["signal"]'s abort reason.
  2. Abort these steps.
5. Initialize and return an AI model object given promise, options, a no-op algorithm, initialize, and create.
Return promise.

To initialize and return an AI model object given a Promise promise, an ordered map options, and algorithms fireProgressEvent, initialize, and create:

Assert: these steps are running in parallel.
Perform fireProgressEvent given 0.
Perform fireProgressEvent given 1.
If performing initialize given options returns false, then:
1. Queue a global task on the AI task source given promise’s relevant global object to reject promise with an "OperationError" DOMException.
2. Return.
Queue a global task on the AI task source given promise’s relevant global object to perform the following steps:
1. If options["signal"] exists and is aborted, then:
  1. Reject promise with options["signal"]'s abort reason.
  2. Abort these steps.
  This check is necessary in case any code running on the event loop caused the AbortSignal to become aborted before this task ran.
2. Let model be the result of performing create given promise’s relevant global object and options.
3. Assert: model implements an interface that includes AIDestroyable.
4. Initialize as a destroyable model.
5. If options["signal"] exists, then add the following abort steps to options["signal"]:
  1. Destroy model given options["signal"]'s abort reason.
6. Resolve promise with model.

6.2. Obtaining results

An error information is a struct used to communicate error information from in parallel to the event loop. It has the following items:

error name: a string that will be used for the DOMException’s name.
error information: other information necessary to create a useful DOMException for the web developer. (Typically, just an exception message.)

To get an aggregated AI model result given an AIDestroyable modelObject, an ordered map options, and an algorithm operation:

If modelObject’s relevant global object is a Window whose associated Document is not fully active, then return a promise rejected with an "InvalidStateError" DOMException.
Let signals be « modelObject’s destruction abort controller’s signal ».
If options["signal"] exists, then append it to signals.
Let compositeSignal be the result of creating a dependent abort signal given signals using AbortSignal and modelObject’s relevant realm.
If compositeSignal is aborted, then return a promise rejected with compositeSignal’s abort reason.
Let abortedDuringOperation be false.

This variable will be written to from the event loop, but read from in parallel.
Add the following abort steps to compositeSignal:
1. Set abortedDuringOperation to true.
Let promise be a new promise created in modelObject’s relevant realm.
In parallel:
1. Let result be the empty string.
2. Let chunkProduced be the following steps given a string chunk:
  1. Queue a global task on the AI task source given modelObject’s relevant global object to perform the following steps:
    1. If abortedDuringOperation is true, then reject promise with compositeSignal’s abort reason.
    2. Otherwise, append chunk to result.
3. Let done be the following steps:
  1. Queue a global task on the AI task source given modelObject’s relevant global object to perform the following steps:
    1. If abortedDuringOperation is true, then reject promise with compositeSignal’s abort reason.
    2. Otherwise, resolve promise with result.
4. Let error be the following steps given error information errorInfo:
  1. Queue a global task on the AI task source given modelObject’s relevant global object to perform the following steps:
    1. If abortedDuringOperation is true, then reject promise with compositeSignal’s abort reason.
    2. Otherwise, reject promise with the result of creating a DOMException with name given by errorInfo’s error name, using errorInfo’s error information to populate the message appropriately.
5. Let stopProducing be the following steps:
  1. Return abortedDuringOperation.
6. Perform operation given chunkProduced, done, error, and stopProducing.
Return promise.

To get a streaming AI model result given an AIDestroyable modelObject, an ordered map options, and an algorithm operation:

If modelObject’s relevant global object is a Window whose associated Document is not fully active, then throw an "InvalidStateError" DOMException.
Let signals be « modelObject’s destruction abort controller’s signal ».
If options["signal"] exists, then append it to signals.
Let compositeSignal be the result of creating a dependent abort signal given signals using AbortSignal and modelObject’s relevant realm.
If compositeSignal is aborted, then return a promise rejected with compositeSignal’s abort reason.
Let abortedDuringOperation be false.

This variable will be written to from the event loop, but read from in parallel.
Add the following abort steps to compositeSignal:
1. Set abortedDuringOperation to true.
Let stream be a new ReadableStream created in this’s relevant realm.
Let canceledDuringOperation be false.

This variable tracks web developer stream cancelations via stream.cancel(), which are not surfaced as errors. It will be written to from the event loop, but sometimes read from in parallel.
Set up stream with cancelAlgorithm set to the following steps (ignoring the reason argument):
1. Set canceledDuringOperation to true.
In parallel:
1. Let chunkProduced be the following steps given a string chunk:
  1. Queue a global task on the AI task source given this’s relevant global object to perform the following steps:
    1. If abortedDuringOperation is true, then error stream with compositeSignal’s abort reason.
    2. Otherwise, enqueue chunk into stream.
2. Let done be the following steps:
  1. Queue a global task on the AI task source given this’s relevant global object to perform the following steps:
    1. If abortedDuringOperation is true, then error stream with compositeSignal’s abort reason.
    2. Otherwise, close stream.
3. Let error be the following steps given error information errorInfo:
  1. Queue a global task on the AI task source given this’s relevant global object to perform the following steps:
    1. If abortedDuringOperation is true, then error stream with compositeSignal’s abort reason.
    2. Otherwise, error stream with the result of creating a DOMException with name given by errorInfo’s error name, using errorInfo’s error information to populate the message appropriately.
4. Let stopProducing be the following steps:
  1. If either abortedDuringOperation or canceledDuringOperation are true, then return true.
  2. Return false.
5. Perform operation given chunkProduced, done, error, and stopProducing.
Return stream.

6.3. Language tags

To validate and canonicalize language tags given a ordered map options and a string key, perform the following steps. They mutate options in place to canonicalize and deduplicate language tags found in options[key], and throw a TypeError if any are invalid.

Assert: options[key] exists.
If options[key] is a string, then set options[key] to the result of validating and canonicalizing a single language tag given options[key].
Otherwise:
1. Assert: options[key] either does not exist, or it is a list of strings.
2. Let languageTags be an empty ordered set.
3. If options[key] exists, then for each languageTag of options[key]:
  1. If IsStructurallyValidLanguageTag(languageTag) is false, then throw a TypeError.
  2. Append the result of validating and canonicalizing a single language tag to languageTags.
4. Set options[key] to languageTags.

To validate and canonicalize a single language tag given a string potentialLanguageTag:

If IsStructurallyValidLanguageTag(potentialLanguageTag) is false, then throw a TypeError.
Return CanonicalizeUnicodeLocaleId(potentialLanguageTag).

To get language availabilities given a description purpose of the purpose for which we’re checking language availability:

Let availabilities be «[ "available" → an empty set, "downloading" → an empty set, "downloadable" → an empty set ]».
For each human language languageTag, represented as a Unicode canonicalized locale identifier, for which the user agent supports purpose, without performing any downloading operations:
1. Append languageTag to availabilities["available"].
For each human language languageTag, represented as a Unicode canonicalized locale identifier, for which the user agent is currently downloading material (e.g., an AI model or fine-tuning) to support purpose:
1. Append languageTag to availabilities["downloading"].
For each human language languageTag, represented as a Unicode canonicalized locale identifier, for which the user agent believes it can support purpose, but only after performing a not-currently-ongoing download (e.g., of an AI model or fine-tuning):
1. Append languageTag to availabilities["downloadable"].
Assert: availabilities["available"], availabilities["downloading"], and availabilities["downloadable"] are disjoint.
If the union of availabilities["available"], availabilities["downloading"], and availabilities["downloadable"] does not meet the language tag set completeness rules, then:
1. Let missingLanguageTags be the set of missing language tags necessary to meet the language tag set completeness rules.
2. For each languageTag of missingLanguageTags:
  1. Append languageTag to one of the three sets. Which of the sets to append to is implementation-defined, and should be guided by considerations similar to that of LookupMatchingLocaleByBestFit in terms of keeping "best fallback languages" together.
3. Return availabilities.

The language tag set completeness rules state that for every item languageTag, if languageTag has more than one subtag, then the set must also contain a less narrow language tag with the same language subtag and a strict subset of the same following subtags (i.e., omitting one or more).

This definition is intended to align with that of [[AvailableLocales]] in ECMAScript Internationalization API Specification. [ECMA-402]

This means that if an implementation supports summarization of "de-DE" input text, it will also count as supporting "de" input text.

The converse direction is supported not by the language tag set completeness rules, but instead by the use of LookupMatchingLocaleByBestFit, which ensures that if an implementation supports summarizing "de" input text, it also counts as supporting summarization of "de-CH", "de-Latn-CH", etc.

6.4. Availability

The minimum availability given a list of AIAvailability-or-null values availabilities is:

If availabilities contains null, then return null.
If availabilities contains "unavailable", then return "unavailable".
If availabilities contains "downloading", then return "downloading".
If availabilities contains "downloadable", then return "downloadable".
Return "available".

6.5. Task source

Tasks queued by this specification use the AI task source.

Writing Assistance APIs

Abstract

Status of this document

1. Introduction

2. Shared APIs

3. The summarizer API

3.1. Creation

3.2. Availability

3.3. The `AISummarizer` class

3.4. Summarization

3.4.1. The algorithm

3.4.2. Options

3.4.3. Errors

4. The writer API

5. The rewriter API

6. Shared infrastructure

6.1. Creation

6.2. Obtaining results

6.3. Language tags

6.4. Availability

6.5. Task source

Index

Terms defined by this specification

Terms defined by reference

References

Normative References

IDL Index

Writing Assistance APIs

Abstract

Status of this document

1. Introduction

2. Shared APIs

3. The summarizer API

3.1. Creation

3.2. Availability

3.3. The AISummarizer class

3.4. Summarization

3.4.1. The algorithm

3.4.2. Options

3.4.3. Errors

4. The writer API

5. The rewriter API

6. Shared infrastructure

6.1. Creation

6.2. Obtaining results

6.3. Language tags

6.4. Availability

6.5. Task source

Index

Terms defined by this specification

Terms defined by reference

References

Normative References

IDL Index

3.3. The `AISummarizer` class