From 7f9326107117bae616fb97e1640b0a2d76c0fa0e Mon Sep 17 00:00:00 2001
From: Bart Veneman <bartveneman@gmail.com>
Date: Tue, 27 Oct 2026 22:07:46 +0100
Subject: [PATCH] fix: calculate specificity of `::highlight` correctly

---
 src/selectors/specificity.test.ts | 32 +++++++++++++++++++++++++++++++
 src/selectors/specificity.ts      | 13 +++++++++++++
 2 files changed, 45 insertions(+)

diff --git a/src/selectors/specificity.test.ts b/src/selectors/specificity.test.ts
index e2f0ec4..0a0a067 100644
--- a/src/selectors/specificity.test.ts
+++ b/src/selectors/specificity.test.ts
@@ -171,6 +171,38 @@ test('handles pseudo element selectors', () => {
 	expect(actual).toEqual(expected)
 })
 
+test('handles the ::part pseudo element', () => {
+	const fixture = `
+    ::part(my-ident),
+    ::part(first-ident second-ident)
+    {}
+  `
+	const actual = analyze(fixture).selectors.specificity.items
+	const expected = [
+		[0, 0, 1],
+		[0, 0, 1],
+	]
+	expect(actual).toEqual(expected)
+})
+
+test('handles the ::highlight pseudo element', () => {
+	const fixture = `
+    ::highlight,
+    ::highlight(),
+    ::highlight(my-ident),
+    ::highlight(*)
+    {}
+  `
+	const actual = analyze(fixture).selectors.specificity.items
+	const expected = [
+		[0, 0, 0],
+		[0, 0, 0],
+		[0, 0, 1],
+		[0, 0, 0],
+	]
+	expect(actual).toEqual(expected)
+})
+
 test('calculates the lowest value', () => {
 	const fixture = `
     #test,
diff --git a/src/selectors/specificity.ts b/src/selectors/specificity.ts
index fe86c32..81b2233 100644
--- a/src/selectors/specificity.ts
+++ b/src/selectors/specificity.ts
@@ -206,6 +206,19 @@ export const calculateForAST = (selectorAST: Selector): Specificity => {
 						break
 					}
 
+					case 'highlight': {
+						if (current.first_child) {
+							// The specificity of a ::highlight() selector with a * argument is zero.
+							if (current.first_child.text === '*') {
+								break
+							}
+							// The specificity of a ::highlight() selector with a <custom-ident> argument
+							// is equivalent to a type selector.
+							c += 1
+						}
+						break
+					}
+
 					default: {
 						c += 1
 						break