fix: escape all special characters in identifiers when stringifying

src/stringify.spec.ts

@@ -28,6 +28,12 @@ describe("Stringify CSS spec compliance", () => {
         ["a\u{7F}b", String.raw`a\7f b`, "DEL character"],
         ["a\u{0}b", String.raw`a\fffd b`, "null → FFFD"],
         ["a'b", String.raw`a\'b`, "single quote"],
+        ["a=b", String.raw`a\=b`, "equals sign"],
+        ["a&b", String.raw`a\&b`, "ampersand"],
+        ["a{b}c", String.raw`a\{b\}c`, "braces"],
+        ["a?b", String.raw`a\?b`, "question mark"],
+        ["a@b", String.raw`a\@b`, "at sign"],
+        ["a`b", String.raw`a\`b`, "backtick"],
     ];
 
     it.each(escapeCases)("%s → %s (%s)", (name, expected) => {
@@ -44,3 +50,18 @@ describe("Stringify CSS spec compliance", () => {
         expect(stringify(ast)).toBe(name);
     });
 });
+
+describe("Stringify round-trips special characters in identifiers", () => {
+    const selectors = [
+        String.raw`.x\&y`,
+        String.raw`[data-foo\=bar]`,
+        String.raw`.a\{b\}c`,
+        String.raw`.w-1\/2`,
+        String.raw`#a\?b`,
+    ];
+    it.each(selectors)("%s", (selector) => {
+        const original = parse(selector);
+        const roundTripped = parse(stringify(original));
+        expect(roundTripped).toStrictEqual(original);
+    });
+});

src/stringify.ts

@@ -32,6 +32,13 @@ const charsToEscapeInName = new Set(
         "/",
         ",",
         ";",
+        "=",
+        "&",
+        "?",
+        "@",
+        "`",
+        "{",
+        "}",
     ].map((c) => c.charCodeAt(0)),
 );