Add the :state() CSS pseudo-class

Author: ddbeck

features/state.yml

@@ -0,0 +1,17 @@
+name: :state()
+description: The `:state()` pseudo-class matches custom elements based on their custom state, set through the `ElementInternals.states` API.
+spec: https://html.spec.whatwg.org/multipage/custom-elements.html#custom-state-pseudo-class
+compat_features:
+  - css.selectors.state
+  - api.CustomStateSet
+  - api.CustomStateSet.@@iterator
+  - api.CustomStateSet.add
+  - api.CustomStateSet.clear
+  - api.CustomStateSet.delete
+  - api.CustomStateSet.entries
+  - api.CustomStateSet.forEach
+  - api.CustomStateSet.has
+  - api.CustomStateSet.keys
+  - api.CustomStateSet.size
+  - api.CustomStateSet.values
+  - api.ElementInternals.states

features/state.yml.dist

@@ -0,0 +1,50 @@
+# Generated from: state.yml
+# Do not edit this file by hand. Edit the source file instead!
+
+status:
+  baseline: low
+  baseline_low_date: 2024-05-17
+  support:
+    chrome: "125"
+    chrome_android: "125"
+    edge: "125"
+    firefox: "126"
+    firefox_android: "126"
+    safari: "17.4"
+    safari_ios: "17.4"
+compat_features:
+  # baseline: low
+  # baseline_low_date: 2024-05-14
+  # support:
+  #   chrome: "90"
+  #   chrome_android: "90"
+  #   edge: "90"
+  #   firefox: "126"
+  #   firefox_android: "126"
+  #   safari: "17.4"
+  #   safari_ios: "17.4"
+  - api.CustomStateSet
+  - api.CustomStateSet.@@iterator
+  - api.CustomStateSet.add
+  - api.CustomStateSet.clear
+  - api.CustomStateSet.delete
+  - api.CustomStateSet.entries
+  - api.CustomStateSet.forEach
+  - api.CustomStateSet.has
+  - api.CustomStateSet.keys
+  - api.CustomStateSet.size
+  - api.CustomStateSet.values
+  - api.ElementInternals.states
+
+  # ⬇️ Same status as overall feature ⬇️
+  # baseline: low
+  # baseline_low_date: 2024-05-17
+  # support:
+  #   chrome: "125"
+  #   chrome_android: "125"
+  #   edge: "125"
+  #   firefox: "126"
+  #   firefox_android: "126"
+  #   safari: "17.4"
+  #   safari_ios: "17.4"
+  - css.selectors.state