Add proposal processes (#543)

* Add proposal processes

Add a new proposal process for API changes. This includes a doc describing
the process and a template from which proposals may be made.

* Update the proposal process with feedback from Rob and Timothy.

---------

Co-authored-by: Devlin Cronin <rdevlin.cronin@chromium.org>

proposals/proposal_process.md

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+# WECG Proposal Process
+
+## Summary
+
+This document outlines a new proposal process for making changes to public
+extension APIs.  This process should be used for all future changes to public
+extension APIs.
+
+## Background and Motivation
+
+Historically, different browsers had (very) different forms of "web extension"
+(also known as "browser extension") platforms, including Chrome Extensions and
+Firefox Add-ons.  Over the past several years, browser vendors have aligned on
+a common set of WebExtension APIs and all major browser vendors (including
+Google Chrome, Mozilla Firefox, and Apple Safari, along with the majority of
+other Chromium-based browsers such as Microsoft Edge, Opera, Brave, and more)
+support the same general API and behavior.
+
+With this convergence on a common platform, browser vendors and developers have
+been working to ensure better cross-browser alignment on new and existing APIs,
+along with future API changes.  This is the primary purpose of the
+[WebExtensions Community
+Group](https://github.com/w3c/webextensions/blob/main/charter.md), or WECG.
+
+However, due to the previous history and implementation practices in which
+every browser had complete autonomy over their own API design and
+implementation, not all APIs and API changes have been brought to the WECG for
+discussion.  At best, this results in a missed opportunity for broader
+community discussion and creates more time between when browsers can support a
+similar API; at worst, this results in significant platform fragmentation, to
+the detriment of the ecosystem.
+
+When changes and proposals have been brought to the WECG, they are frequently
+presented in different formats and manners based on historical precedence for a
+specific browser.  This makes it more difficult to review, as well as risking
+the omission of important criteria or details.
+
+In order to address these concerns, we use a defined and consistent
+proposal process.
+
+## Goals
+
+**Provide a consistent path for proposing new APIs and API modifications.**
+The new process should be scalable to be used for both entirely new APIs as
+well as the introduction of new methods on an existing API namespace or
+modifications to behavior of existing APIs.
+
+**Include critical details in each API proposal.**  There are a set of common
+concerns that should be addressed in any and all API additions and changes.
+These include categories such as security, privacy, web compatibility, and
+others.
+
+**Ensure browsers can retain autonomy for certain APIs.**  The WECG outlines
+that browsers always have the ability to innovate on their own or create
+individual APIs that are not supported by other browsers (such as when an API
+is for a browser-specific surface or feature that no other browser intends to
+provide).  This proposal process should not hinder that.
+
+**Supplement browser-specific proposal processes.**  We understand that
+individual browser vendors will very likely have their own proposal processes
+for these APIs (e.g. to do internal review, address UI elements, etc).  The
+WECG proposal should serve as a productive supplement to those discussions,
+ideally reducing or eliminating duplicate work.
+
+## Non-Goals
+
+**Replace issue reporting for suggested features or changes.**  The API
+proposal should be viewed as a possible "next step" from a suggested change or
+developer issue and should imply that one or more browser vendors are actively
+or imminently going to begin implementation.  Most feature requests and bug
+reports should continue to be reported as GitHub issues in the WECG repository
+(or a browser's individual bug tracker).
+
+**Address all implementation details.**  Due to the dramatically different
+implementations in different browsers, the vast majority of implementation
+details are out of scope for the API proposal.  These may still be included if
+they have cross-browser implications (such as the use of a given technology
+that will be tied to the capabilities of the API or algorithms that would
+affect the developer-visible surface).
+
+**Address all browser-specific considerations.**  Very likely, individual
+browsers will have separate design docs detailing the browser-specific aspects
+of the API.  These are out of scope of the WECG.  If appropriate, the author
+may include browser-specific considerations as addenda or useful background.
+
+**Replace a proper, detailed, web-style spec.**  While we do not currently have
+complete specs for extension APIs, we intend to (gradually) produce them.
+These API proposals should deal with higher-level discussion of the API as a
+whole, and should not include exact spec language.
+
+**Have API proposals be perennially "living" documents.**  An API proposal
+should be kept up-to-date during the implementation period of the initial API
+or change it proposes.  Once that initial version or change has been
+implemented, the proposal is complete.  Any changes should have a separate
+proposal.
+
+## Prior Art
+
+This proposal is heavily inspired by the existing
+[Chrome Extension API Proposal Process](https://chromium.googlesource.com/chromium/src/+/HEAD/extensions/docs/new_api_proposal.md)
+and [API Overview Document](https://docs.google.com/document/d/182XXEPwbh5dyMTO_Q3bZ9k4PYY19Woydu5b3XvPoSmc/edit#heading=h.x9snb54sjlu9)
+(which has been used for many new extension APIs and has been a jumping off
+point for some new proposals in the WECG).
+
+## When to Use this Proposal
+
+This proposal should be used for any significant new changes or additions to
+public extension APIs.
+
+## When to Not Use this Proposal
+
+Browsers do not need to use this proposal for any APIs that will never become
+public.  As an example, in Chrome, there is the concept of "private APIs" that
+are used by [component extensions](https://chromium.googlesource.com/chromium/src/+/main/extensions/docs/component_extensions.md)
+-- extensions that are built into the browser as an implementation detail.  In
+these cases, browser vendors do not need to (and should not!) put forth an API
+proposal in this forum.  (Though note that browsers may still have separate
+processes for such APIs.)
+
+## How to Use this Proposal
+
+*   Find (or represent) a browser willing to implement the API imminently and
+    propose the API.  We want to ensure these API proposals don't become a
+    collection of "aspirational" APIs -- things that we would ideally like to
+    get to at some point.  These proposals should have thorough (and thus,
+    potentially costly) reviews, beyond what we expect for a general overview
+    of a suggestion in a filed issue.  As such, these proposals should only be
+    used for APIs that have support and commitment to implement from at least
+    one browser.
+*   Copy the [API Proposal template](proposal_template.md) and fill it out.  
+    There are instructions in each section of the proposal template.  As you
+    fill out each section, you may delete the instructions for that section.
+    For any section that is not relevant, you may put "N/A" (likely with a
+    brief summary of why the section is not relevant, if it is not immediately
+    obvious).
+*   Submit a pull request with the completed proposal to the
+    [Proposals directory](https://github.com/w3c/webextensions/tree/main/proposals)
+    of the WECG repository.
+*   Receive and iterate on input from browser vendors and the community.
+*   Once every browser vendor has indicated their support or opposition (see
+    below) and all major comments are resolved, the proposal may be merged and
+    considered "complete".
+
+## Browser Vendor Support
+
+Browser vendors should provide input on the proposal and indicate their level
+of support with the existing browser-specific
+[labels](https://github.com/w3c/webextensions/labels) or a new
+"changes-requested" label.
+
+*   **Supportive:** The browser vendor is supportive of the API design and may
+    implement the API in the future.  Note that this is not a guarantee the
+    browser _will_ add support at any given moment and time.
+*   **Neutral:** The browser vendor neither supports nor opposes the API design
+    and may implement the API in the future.
+*   **Opposed:** The browser vendor is opposed to the API design at a
+    fundamental level (that is, they do not believe such an API should exist on
+    the extensions platform) and has no plans to implement the API in the
+    future.
+*   **Changes-Requested:** The browser vendor is potentially supportive (or at
+    the very least, is not opposed) to the API, but would like to see
+    non-trivial changes to the proposal before it moves forward, such as
+    changing the API surface or types.
+
+API proposals should not be considered "complete" until all major browser
+vendors have entered a value other than "changes-requested".  Unanimous support
+is _not_ required for API proposals to proceed, as a core tenant of the WECG is
+that browsers may use extension APIs for browser-specific functionality.
+Browser vendors should ensure reasonable response times; if a browser vendor
+does not respond in a timely manner, the proposal may move forward.  There is
+no strict definition of this; it is adhered to with good faith effort by the
+participating browsers for the applicable APIs.  However, if we see this being
+abused, we may reconsider this approach.
+
+### Opposition
+
+Browser vendors that are opposed to the API may still offer input on the API if
+they desire (we fully acknowledge that everyone working in this space is
+experienced and may have valuable input on API designs, even if they don't
+agree with the functionality).
+
+It may happen that the proposing browser vendor (again, every proposal must be
+sponsored by a browser vendor) and a reviewing browser vendor are unable to
+reach consensus (with regard to either the API's concept or an individual
+aspect of it).  In this scenario, the reviewing vendor must choose a stance
+(which will very likely be "Opposed") to allow the API to move forward.

proposals/proposal_template.md

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+# Proposal: <API>
+
+** How to Use This Template **
+
+See [Proposal Process](proposal_process.md) for the detailed process on how to
+propose new APIs and use this template.  Each section includes instructions on
+what to include.  Delete the instructions for a given section once it's filled
+out.  Remove this section once the template is filled out.
+
+**Summary**
+
+An API proposal for your new API.  Describe in **one sentence** what it will be
+used for.
+
+**Document Metadata**
+
+**Author:** <your Github handle>
+
+**Sponsoring Browser:** The browser vendor committed to implementing this API
+if approved.
+
+**Contributors:** <other contributors emails or GitHub handles>
+
+**Created:** YYYY-MM-DD
+
+**Related Issues:** <urls>
+
+## Motivation
+
+### Objective
+
+What does this API enable?  Why do we need it?
+
+#### Use Cases
+
+Describe the use cases for this API.  There may be multiple.
+
+### Known Consumers
+
+APIs should, ideally, have significant adoption once they are complete.
+Highlight any extensions that have committed to using this API.
+
+## Specification
+
+### Schema
+
+Include your API schema here (preferably with a TypeScript interface).  If you
+are adding new functionality or fields to an existing method, please be sure to
+call out explicitly what has changed.
+
+A few notes:
+
+*   Extension APIs are almost always asynchronous.  In most browsers, extensions
+    run in a separate child process for security purposes.  Anything that cannot
+    be resolved directly in a child process must be asynchronous, and even if
+    something can be done in a child process today, it should frequently be
+    asynchronous to prevent future breakage if we move something to the parent
+    process.
+*   Failures should be indicated by either synchronously throwing an error
+    (rare) or rejecting the returned promise.  (Note that in legacy versions,
+    this will populate
+    [chrome.runtime.lastError](https://developer.chrome.com/extensions/runtime#property-lastError).)
+    Do not provide another mechanism of indicating failure (e.g., don't accept
+    a failure callback).
+*   When practical, prefer accepting objects for input parameters.  This allows
+    us to expand APIs in the future in a non-breaking change by adding
+    additional optional properties.  Even if you currently only accept one
+    property, it often makes sense to wrap this in an object.
+
+### New Permissions
+
+| Permission Added | Suggested Warning |
+| ---------------- | ----------------- |
+| New Permission 1 | Add a proposed warning string for the permission.  If there should be no warning, provide justification as to why. Browser vendors can ultimately choose if there should be a warning and what it should be independently, but this can be useful to define especially if it has implications for the likelihood this proposal will succeed or be useful to developers. |
+
+Document any new permission added by this API.  Permissions are frequently the
+same as the API itself, e.g. the `browser.storage` API has the permission
+"storage".
+
+If this is a new API, it should add a new permission.  A new permission does
+_not_ always require a new permission warning (though it should frequently have
+one).  Adding a permission allows us to statically analyze extensions with
+greater accuracy, and avoid exposing unnecessary APIs.
+
+If this is a modification to an existing API, it _may_ require a new permission
+if the capabilities it adds are significantly different than the existing
+functionality in the API, and not already covered by the permission warning.
+Note that this is generally an indication that this might be better as a new
+API than a modification to an existing API.  If no new permission is needed,
+note why this falls within the current bounds of the API's capabilities.
+
+### Manifest File Changes
+
+Document if your API will require additional manifest fields to be added or
+modified (other than a new permission), and what they will do.  If non-trivial,
+describe the validation and error handling.  When a failure is not critical,
+prefer a soft warning over a hard error.  Hard errors will prevent the extension
+from loading, which makes it more challenging to change or expand behavior in
+the future.
+
+If there are no new manifest fields, indicate so here.
+
+## Security and Privacy
+
+### Exposed Sensitive Data
+
+Document any sensitive data or personally-identifiable information the API
+exposes to the extension.
+
+### Abuse Mitigations
+
+Extension APIs are very frequently powerful and scary (which is one of the
+primary reasons they cannot be exposed to the open web).  Highlight any ways
+this API could be abused by extensions using it.  These should describe ways
+that the API could be potentially abused that are _not_ bugs in the browser.
+(For instance, stealing PII that is provided through the API is not a bug in
+the browser, but is an avenue for abuse.)
+
+Describe how these scenarios will be mitigated.  Examples include restricting
+based on user action, increased attribution, visual disclosure to the user,
+etc.
+
+### Additional Security Considerations
+
+Highlight any additional security considerations in the design of this API.
+Consider process sandboxing, any input that needs to be sanitized, what can
+happen in the case of a compromised process, and other potential attack
+vectors.
+
+## Alternatives
+
+### Existing Workarounds
+
+Describe any workarounds that exist today.  If this API did not exist, what
+approach could developers take to solve the same use cases?
+
+### Open Web API
+
+Extensions are designed to be "The Web + More", not an alternative to the web.
+Additionally, an Open Web API is generally preferred when possible, because
+they allow the utility to be shared by extensions, websites, Progressive Web
+Apps, and more.
+
+Describe why this API does not belong on the open web.
+
+## Implementation Notes
+
+If there are any significant notes on implementation that are relevant across
+browsers, please indicate them here.  (Feel free to add more sections.)
+
+## Future Work
+
+Highlight any planned or prospective future work.