Add holding features for unspecified platform features

features/draft/unspecified-apis.yml

@@ -0,0 +1,28 @@
+draft_date: 2025-02-20
+name: Unspecified APIs
+description: Some browsers implement unspecified APIs. This is an artificial feature that contains references to browser compatibility data entries for those additions.
+spec: https://web-platform-dx.github.io/unspecified/
+discouraged:
+  according_to:
+    - https://web-platform-dx.github.io/unspecified/
+compat_features:
+  # Chrome implemented these APIs while they were in a PR for the spec, which
+  # was subsequently not included in the ultimately merged changes.
+  # https://github.com/w3c/payment-handler/pull/170#issuecomment-483453062
+  # https://issues.chromium.org/issues/40527525
+  - api.AbortPaymentEvent
+  - api.AbortPaymentEvent.AbortPaymentEvent
+  - api.AbortPaymentEvent.respondWith
+
+  # These `Screen` properties are broadly interoperable but unspecified.
+  # https://github.com/w3c/window-management/pull/76#discussion_r780596068
+  # contains the only discussion I could find of this fact.
+  - api.Screen.availLeft
+  - api.Screen.availLeft.relative-multi-screen
+  - api.Screen.availTop
+  - api.Screen.availTop.relative-multi-screen
+
+  # Dropped from Accessibility Object Model spec and potentially never shipped
+  # anywhere. https://wicg.github.io/aom/spec/phase2.html#privacy-concerns
+  # https://github.com/mdn/browser-compat-data/pull/25860
+  - api.Permissions.permission_accessibility-events

features/draft/unspecified-apis.yml.dist

@@ -0,0 +1,44 @@
+# Generated from: unspecified-apis.yml
+# Do not edit this file by hand. Edit the source file instead!
+
+status:
+  baseline: false
+  support: {}
+compat_features:
+  # baseline: high
+  # baseline_low_date: 2020-01-15
+  # baseline_high_date: 2022-07-15
+  # support:
+  #   chrome: "1"
+  #   chrome_android: "18"
+  #   edge: "79"
+  #   firefox: "1"
+  #   firefox_android: "4"
+  #   safari: "1"
+  #   safari_ios: "1"
+  - api.Screen.availLeft
+  - api.Screen.availTop
+
+  # baseline: false
+  # support:
+  #   chrome: "1"
+  #   chrome_android: "18"
+  #   edge: "79"
+  #   firefox: "1"
+  #   firefox_android: "4"
+  - api.Screen.availLeft.relative-multi-screen
+  - api.Screen.availTop.relative-multi-screen
+
+  # baseline: false
+  # support:
+  #   chrome: "70"
+  #   chrome_android: "70"
+  #   edge: "79"
+  - api.AbortPaymentEvent
+  - api.AbortPaymentEvent.AbortPaymentEvent
+  - api.AbortPaymentEvent.respondWith
+
+  # ⬇️ Same status as overall feature ⬇️
+  # baseline: false
+  # support: {}
+  - api.Permissions.permission_accessibility-events

features/draft/unspecified-css.yml

@@ -0,0 +1,10 @@
+draft_date: 2025-02-20
+name: Unspecified CSS
+description: Some browsers implement unspecified CSS properties or values. This is an artificial feature that contains references to browser compatibility data entries for those additions.
+spec: https://web-platform-dx.github.io/unspecified/
+discouraged:
+  according_to:
+    - https://web-platform-dx.github.io/unspecified/
+compat_features:
+  # Removed from the platform, but not yet removed from BCD
+  - -moz-image-region # To be removed in March 2025

features/draft/unspecified-css.yml.dist

@@ -0,0 +1,8 @@
+# Generated from: unspecified-css.yml
+# Do not edit this file by hand. Edit the source file instead!
+
+status:
+  baseline: false
+  support: {}
+compat_features:
+  - -moz-image-region

features/draft/unspecified-html.yml

@@ -0,0 +1,12 @@
+draft_date: 2025-02-20
+name: Unspecified HTML
+description: Some browsers implement unspecified HTML elements and attributes. This is an artificial feature that contains references to browser compatibility data entries for those additions.
+spec: https://web-platform-dx.github.io/unspecified/
+discouraged:
+  according_to:
+    - https://web-platform-dx.github.io/unspecified/
+compat_features:
+  # Stuck in WHATWG PR limbo:
+  # https://github.com/mdn/browser-compat-data/pull/25863
+  - api.HTMLAnchorElement.hrefTranslate
+  - html.elements.a.hreftranslate

features/draft/unspecified-html.yml.dist

@@ -0,0 +1,11 @@
+# Generated from: unspecified-html.yml
+# Do not edit this file by hand. Edit the source file instead!
+
+status:
+  baseline: false
+  support:
+    chrome: "81"
+    chrome_android: "81"
+compat_features:
+  - api.HTMLAnchorElement.hrefTranslate
+  - html.elements.a.hreftranslate

features/draft/unspecified-javascript.yml

@@ -0,0 +1,29 @@
+draft_date: 2025-02-20
+name: Unspecified JavaScript
+description: Some browsers implement unspecified JavaScript properties or methods. This is an artificial feature that contains references to browser compatibility data entries for those additions.
+spec: https://web-platform-dx.github.io/unspecified/
+discouraged:
+  according_to:
+    - https://web-platform-dx.github.io/unspecified/
+compat_features:
+  # Firefox-only Function property.
+  # There exists some discussion of getting rid
+  # of it: https://github.com/tc39/proposal-error-stacks/issues/14
+  - javascript.builtins.Function.displayName
+
+  # Firefox-only InternalError object
+  # Thrown on "too much recursion" while Safari and Chrome throw RangeError
+  # https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Too_much_recursion
+  - javascript.builtins.InternalError
+  - javascript.builtins.InternalError.InternalError
+
+  # Firefox-only Error properties
+  - javascript.builtins.Error.Error.lineNumber_parameter
+  - javascript.builtins.Error.lineNumber
+  - javascript.builtins.Error.Error.fileName_parameter
+  - javascript.builtins.Error.fileName
+  - javascript.builtins.Error.columnNumber
+
+  # Error.prototype.stack is a candidate for future standardization
+  # https://github.com/tc39/proposal-error-stacks
+  - javascript.builtins.Error.stack

features/draft/unspecified-javascript.yml.dist

@@ -0,0 +1,40 @@
+# Generated from: unspecified-javascript.yml
+# Do not edit this file by hand. Edit the source file instead!
+
+status:
+  baseline: false
+  support:
+    firefox: "13"
+    firefox_android: "14"
+compat_features:
+  # baseline: high
+  # baseline_low_date: 2015-07-29
+  # baseline_high_date: 2018-01-29
+  # support:
+  #   chrome: "3"
+  #   chrome_android: "18"
+  #   edge: "12"
+  #   firefox: "1"
+  #   firefox_android: "4"
+  #   safari: "6"
+  #   safari_ios: "6"
+  - javascript.builtins.Error.stack
+
+  # baseline: false
+  # support:
+  #   firefox: "1"
+  #   firefox_android: "4"
+  - javascript.builtins.Error.Error.fileName_parameter
+  - javascript.builtins.Error.Error.lineNumber_parameter
+  - javascript.builtins.Error.columnNumber
+  - javascript.builtins.Error.fileName
+  - javascript.builtins.Error.lineNumber
+  - javascript.builtins.InternalError
+  - javascript.builtins.InternalError.InternalError
+
+  # ⬇️ Same status as overall feature ⬇️
+  # baseline: false
+  # support:
+  #   firefox: "13"
+  #   firefox_android: "14"
+  - javascript.builtins.Function.displayName

gh-pages/src/unspecified.md

@@ -0,0 +1,12 @@
+---
+layout: "default.html"
+title: Unspecified web platform features
+---
+
+Some browsers implement additions to HTML, CSS, JavaScript, and web APIs that are not part of any known web platform specification, past or present, such as the specifications published by the [W3C](https://www.w3.org/standards/), [TC39](https://tc39.es/), or [WHATWG](https://whatwg.org/). Typically, these are historic additions, retained for backwards compatibility.
+
+**If you're a web developer, think carefully before relying on these features.** They usually have poor cross-browser support, surprising behaviors, and limited documentation.
+
+Since these additions are unspecified and rarely supported across browsers, web-features reports these additions as having limited availability. Also, web-features deems the features as [discouraged](https://github.com/web-platform-dx/web-features/blob/main/docs/guidelines.md#discouraged) by omission from relevant specifications.
+
+If you're a browser implementer or specification editor and you think a feature has been marked as unspecified in error, [file an issue on web-platform-dx/web-features](https://github.com/web-platform-dx/web-features/issues).

scripts/specs.ts

@@ -120,6 +120,10 @@ const defaultAllowlist: allowlistItem[] = [
     [
         "https://github.com/MicrosoftEdge/MSEdgeExplainers/blob/main/DocumentSubtitle/explainer.md",
         "Allowed because this is where the application-title meta tag is spec'd at the moment. Remove when https://github.com/whatwg/html/issues/8909 is fixed."
+    ],
+    [
+        "https://web-platform-dx.github.io/unspecified/",
+        "Allowed as a fallback for unspecified- features."
     ]
 ];