Set selector syntax to selector name when possible

src/browserlib/extract-cssdfn.mjs

@@ -306,6 +306,21 @@ export default function () {
     delete value.pureSyntax;
   }
 
+  // Specs typically do not make the syntax of selectors such as `:visited`
+  // explicit because it essentially goes without saying: the syntax is the
+  // selector's name itself. Note that the syntax of selectors that are
+  // function-like such as `:nth-child()` cannot be inferred in the same way.
+  for (const selector of res.selectors) {
+    if (!selector.value && !selector.name.match(/\(/)) {
+      selector.value = selector.name;
+    }
+    for (const subSelector of selector.values ?? []) {
+      if (!subSelector.value && !subSelector.name.match(/\(/)) {
+        subSelector.value = subSelector.name;
+      }
+    }
+  }
+
   // Report warnings
   if (warnings.length > 0) {
     res.warnings = warnings;

test/extract-css.js

@@ -668,11 +668,13 @@ that spans multiple lines */
     css: [
       {
         name: ":open",
-        prose: "The :open pseudo-class represents an element that has both “open” and “closed” states, and which is currently in the “open” state."
+        prose: "The :open pseudo-class represents an element that has both “open” and “closed” states, and which is currently in the “open” state.",
+        value: ":open"
       },
       {
         name: ":closed",
-        prose: "The :closed pseudo-class represents an element that has both “open” and “closed” states, and which is currently in the “closed” state."
+        prose: "The :closed pseudo-class represents an element that has both “open” and “closed” states, and which is currently in the “closed” state.",
+        value: ":closed"
       }
     ]
   },
@@ -1234,10 +1236,12 @@ that spans multiple lines */
     css: [{
       name: '::first-letter',
       prose: 'The ::first-letter pseudo-element represents the first letter.',
+      value: '::first-letter',
       values: [{
         name: '::prefix',
         type: 'selector',
-        prose: 'The ::prefix represents the preceding punctuation of the ::first-letter element.'
+        prose: 'The ::prefix represents the preceding punctuation of the ::first-letter element.',
+        value: '::prefix'
       }]
     }]
   },