diff --git a/apps/oxfmt/conformance/snapshots/prettier.snap.md b/apps/oxfmt/conformance/snapshots/prettier.snap.md
index c0b1cabfe5..99d3d1d29f 100644
--- a/apps/oxfmt/conformance/snapshots/prettier.snap.md
+++ b/apps/oxfmt/conformance/snapshots/prettier.snap.md
@@ -294,32 +294,32 @@
 
 ### Error
 
-- externals/prettier/css/atrule/charset.css: Syntax error: expect token `<string>`, but found `<ident>`
-  - ❓unclassified
-- externals/prettier/css/atrule/import.css: Syntax error: expect token `<ident>`, but found `(`
-  - ❓unclassified
 - externals/prettier/css/atrule/supports.css: Syntax error: expect token `)`, but found `<`
   - ❓unclassified
+- externals/prettier/css/atrule/charset.css: Syntax error: expect token `<string>`, but found `<ident>`
+  - crates/oxc_formatter_css/DIVERGENCES.md#grammar-owner-rejected
+- externals/prettier/css/atrule/import.css: Syntax error: expect token `<ident>`, but found `(`
+  - crates/oxc_formatter_css/DIVERGENCES.md#grammar-owner-rejected
 - externals/prettier/css/attribute/quotes.css: Syntax error: expect token `]`, but found `(`
-  - ❓unclassified
+  - crates/oxc_formatter_css/DIVERGENCES.md#grammar-owner-rejected
 - externals/prettier/css/combinator/combinator.css: Syntax error: expect token `{`, but found `/`
-  - ❓unclassified
+  - crates/oxc_formatter_css/DIVERGENCES.md#grammar-owner-rejected
 - externals/prettier/css/comments/selectors.css: Syntax error: simple selector is expected
-  - ❓unclassified
+  - crates/oxc_formatter_css/DIVERGENCES.md#grammar-owner-rejected
 - externals/prettier/css/custom-properties/emoji.css: Syntax error: declaration at top level is disallowed
-  - ❓unclassified
+  - crates/oxc_formatter_css/DIVERGENCES.md#grammar-owner-rejected
 - externals/prettier/css/no-semicolon/url.css: Syntax error: URL is expected
-  - ❓unclassified
+  - crates/oxc_formatter_css/DIVERGENCES.md#grammar-owner-rejected
 - externals/prettier/css/postcss-plugins/postcss-mixins.css: Syntax error: expect token `{`, but found `<unknown>`
-  - ❓unclassified
+  - crates/oxc_formatter_css/DIVERGENCES.md#grammar-owner-rejected
 - externals/prettier/css/postcss-plugins/postcss-simple-vars.css: Syntax error: declaration at top level is disallowed
-  - ❓unclassified
+  - crates/oxc_formatter_css/DIVERGENCES.md#grammar-owner-rejected
 - externals/prettier/css/quotes/quotes.css: Syntax error: expect token `{`, but found `<string>`
-  - ❓unclassified
+  - crates/oxc_formatter_css/DIVERGENCES.md#grammar-owner-rejected
 - externals/prettier/css/selector-list/selectors.css: Syntax error: simple selector is expected
-  - ❓unclassified
+  - crates/oxc_formatter_css/DIVERGENCES.md#grammar-owner-rejected
 - externals/prettier/css/selector-string/string.css: Syntax error: simple selector is expected
-  - ❓unclassified
+  - crates/oxc_formatter_css/DIVERGENCES.md#grammar-owner-rejected
 
 ## scss
 
@@ -366,20 +366,20 @@
 
 ### Error
 
-- externals/prettier/css/custom-properties/emoji.css: Syntax error: declaration at top level is disallowed
-  - ❓unclassified
-- externals/prettier/scss/atrule/for.scss: Syntax error: Sass keyword `to` is expected
-  - ❓unclassified
 - externals/prettier/scss/case/case.scss: Syntax error: expect token `<string>`, but found `<ident>`
   - ❓unclassified
+- externals/prettier/css/custom-properties/emoji.css: Syntax error: declaration at top level is disallowed
+  - crates/oxc_formatter_css/DIVERGENCES.md#grammar-owner-rejected
+- externals/prettier/scss/atrule/for.scss: Syntax error: Sass keyword `to` is expected
+  - crates/oxc_formatter_css/DIVERGENCES.md#grammar-owner-rejected
 - externals/prettier/scss/comments/CRLF.scss: Syntax error: component value is expected
-  - ❓unclassified
+  - crates/oxc_formatter_css/DIVERGENCES.md#grammar-owner-rejected
 - externals/prettier/scss/math/3945.scss: Syntax error: declaration at top level is disallowed
-  - ❓unclassified
+  - crates/oxc_formatter_css/DIVERGENCES.md#grammar-owner-rejected
 - externals/prettier/scss/no-semicolon/url.scss: Syntax error: expect token `<string>`, but found `<ident>`
-  - ❓unclassified
+  - crates/oxc_formatter_css/DIVERGENCES.md#grammar-owner-rejected
 - externals/prettier/scss/parens/parens.scss: Syntax error: component value is expected
-  - ❓unclassified
+  - crates/oxc_formatter_css/DIVERGENCES.md#grammar-owner-rejected
 
 ## less
 
@@ -423,20 +423,20 @@
 
 ### Error
 
-- externals/prettier/less/case/case.less: Syntax error: expect token `(`, but found `<ident>`
-  - ❓unclassified
-- externals/prettier/less/comments/in-value.less: Syntax error: expect token `;`, but found `{`
-  - ❓unclassified
-- externals/prettier/less/interpolation/interpolation.less: Syntax error: expect token `<ident>`, but found `@{`
-  - ❓unclassified
 - externals/prettier/less/less/less.less: Syntax error: expect one of `<ident>` or `@{`, but found `(`
   - ❓unclassified
-- externals/prettier/less/lookup/lookup-1.less: Syntax error: expect token `;`, but found `<ident>`
-  - ❓unclassified
-- externals/prettier/less/no-semicolon/url.less: Syntax error: expect token `(`, but found `<ident>`
-  - ❓unclassified
 - externals/prettier/less/parens/parens.less: Syntax error: expect token `;`, but found `{`
   - ❓unclassified
+- externals/prettier/less/case/case.less: Syntax error: expect token `(`, but found `<ident>`
+  - crates/oxc_formatter_css/DIVERGENCES.md#grammar-owner-rejected
+- externals/prettier/less/comments/in-value.less: Syntax error: expect token `;`, but found `{`
+  - crates/oxc_formatter_css/DIVERGENCES.md#grammar-owner-rejected
+- externals/prettier/less/interpolation/interpolation.less: Syntax error: expect token `<ident>`, but found `@{`
+  - crates/oxc_formatter_css/DIVERGENCES.md#grammar-owner-rejected
+- externals/prettier/less/lookup/lookup-1.less: Syntax error: expect token `;`, but found `<ident>`
+  - crates/oxc_formatter_css/DIVERGENCES.md#grammar-owner-rejected
+- externals/prettier/less/no-semicolon/url.less: Syntax error: expect token `(`, but found `<ident>`
+  - crates/oxc_formatter_css/DIVERGENCES.md#grammar-owner-rejected
 
 ## graphql
 
diff --git a/crates/oxc_formatter_css/AGENTS.md b/crates/oxc_formatter_css/AGENTS.md
index 6e74d29b7e..6ef180cc8c 100644
--- a/crates/oxc_formatter_css/AGENTS.md
+++ b/crates/oxc_formatter_css/AGENTS.md
@@ -193,7 +193,7 @@ and a host-supplied `TailwindSorter` does the ordering and dedup outside this cr
 Covered: `$var: value !important;` declarations (root and inside rules), `$var` references in property values and at-rule preludes,
 `$(var)` interpolation in property names.
 
-NOT covered: `$(var)` interpolation inside values and selectors (`.icon.is-$(network)`), selector-position bare `$var` (`.$prefix`), comment substitutions (`<<$(var)>>`).
+NOT covered: `$(var)` interpolation inside values and selectors (`.icon.is-$(network)`, rejected: DIVERGENCES.md#grammar-owner-rejected), selector-position bare `$var` (`.$prefix`), comment substitutions (`<<$(var)>>`).
 
 ## Verification
 
diff --git a/crates/oxc_formatter_css/DIVERGENCES.md b/crates/oxc_formatter_css/DIVERGENCES.md
index 4ff1220f7e..9324fef4a3 100644
--- a/crates/oxc_formatter_css/DIVERGENCES.md
+++ b/crates/oxc_formatter_css/DIVERGENCES.md
@@ -1026,10 +1026,33 @@ our core `fill` (biome semantics) breaks only at the last fitting separator.
 Layout-only, the principled fix is the shared core-fill fit-check change (needs a JS-conformance impact experiment first).
 A spaced `/` is not part of this: it glues to its left operand and breaks after, as in Prettier (`tests/fixtures/format/css/fill-math-chunk-break.css`).
 
-## less-value-interpolation-rejected
+## grammar-owner-rejected
 
-- Why: uniform-rule (error semantics)
+- Why: uniform-rule (acceptance: the grammar owner decides)
 - Pin: `tests/fixtures/mod.rs::parse_error_is_err` (parser-level: the rejection is asserted directly)
+- Conformance:
+  - `externals/prettier/css/atrule/charset.css`
+  - `externals/prettier/css/atrule/import.css`
+  - `externals/prettier/css/attribute/quotes.css`
+  - `externals/prettier/css/combinator/combinator.css`
+  - `externals/prettier/css/comments/selectors.css`
+  - `externals/prettier/css/custom-properties/emoji.css`
+  - `externals/prettier/css/no-semicolon/url.css`
+  - `externals/prettier/css/postcss-plugins/postcss-mixins.css`
+  - `externals/prettier/css/postcss-plugins/postcss-simple-vars.css`
+  - `externals/prettier/css/quotes/quotes.css`
+  - `externals/prettier/css/selector-list/selectors.css`
+  - `externals/prettier/css/selector-string/string.css`
+  - `externals/prettier/scss/atrule/for.scss`
+  - `externals/prettier/scss/comments/CRLF.scss`
+  - `externals/prettier/scss/math/3945.scss`
+  - `externals/prettier/scss/no-semicolon/url.scss`
+  - `externals/prettier/scss/parens/parens.scss`
+  - `externals/prettier/less/case/case.less`
+  - `externals/prettier/less/comments/in-value.less`
+  - `externals/prettier/less/interpolation/interpolation.less`
+  - `externals/prettier/less/lookup/lookup-1.less`
+  - `externals/prettier/less/no-semicolon/url.less`
 
 ```less
 /* input */
@@ -1043,9 +1066,18 @@ A spaced `/` is not part of this: it glues to its left operand and breaks after,
 }
 ```
 
-Value-position `@{var}` interpolation: `oxc-css-parser` rejects it matching `lessc`;
-Prettier (postcss) accepts and prints verbatim. Per the policy's "Error semantics",
-we never format what the reference compiler rejects (a parse error is the SAFE failure).
+`oxc-css-parser` rejects what the variant's grammar owner rejects (oxc-css-parser AGENTS.md "Acceptance"),
+so per the policy's "Error semantics" we leave it as-is (a parse error is the SAFE failure);
+Prettier (postcss) accepts these and prints them, mostly verbatim.
+
+- CSS, a browser drops the rule (Chrome; lightningcss, built on `cssparser`):
+  - invalid selectors: `a[id=func("foo")]`, `-Option/root .a`, `>>>`, `.is-$(var)`, `:not(".a")`, `one "two" three`
+  - invalid `@import` preludes: `@import (multiple) "a";`, `@import "a" {}`
+  - root declarations, `--foo: { }` included (a custom property, not the raw-prelude `x: { }` rule)
+  - `@charset UTF-8;`: only the exact `@charset "...";` form means anything (css-syntax-3); a browser drops both forms, so this one rests on the spec
+- SCSS, dart-sass rejects: `@for $i from 1 end 3`, a Less variable (`@var`) in a value, root declarations
+- Less, lessc rejects: value-position `@{var}`, SCSS interpolation (`#{$var}`), `@IMPORT a;`, a spaced lookup (`@c [ a ]`), `++1`
+- Every owner rejects `@import ur l(a.css);`
 
 ## media-query-operator-spacing
 
diff --git a/crates/oxc_formatter_css/tests/fixtures/mod.rs b/crates/oxc_formatter_css/tests/fixtures/mod.rs
index 20e23cc8c0..bacd10bc49 100644
--- a/crates/oxc_formatter_css/tests/fixtures/mod.rs
+++ b/crates/oxc_formatter_css/tests/fixtures/mod.rs
@@ -184,8 +184,31 @@ fn parse_error_is_err() {
         // when a declaration's value hits a top-level `{` (name + `:` parsed);
         // a selector error with no such head stays a hard error.
         ("a, { color: red; }", css),
-        // Pin for crates/oxc_formatter_css/DIVERGENCES.md#less-value-interpolation-rejected
+        // Pin for crates/oxc_formatter_css/DIVERGENCES.md#grammar-owner-rejected, one input per shape.
+        // CSS: a browser drops the rule
+        ("a[id=func(\"foo\")] {}", css),
+        ("-Option/root .a {}", css),
+        (".a >>> .b {}", css),
+        (".icon.is-$(network) {}", css),
+        (":not(\".a\") {}", css),
+        ("one \"two\" three {}", css),
+        ("@import (multiple) \"a.less\";", css),
+        ("@import \"a.css\" {}", css),
+        ("@import ur l(a.css);", css),
+        ("color: red;", css),
+        ("--foo: { color: red; }", css),
+        ("@charset UTF-8;", css),
+        // SCSS: dart-sass rejects (root declarations: `display: flex;` above)
+        ("@for $i from 1 end 3 {}", scss),
+        ("a { color: @var; }", scss),
+        ("@import ur l(a.css);", scss),
+        // Less: lessc rejects
         (".a { width: @{min-width}; }", less),
+        (".a { width: #{$var}; }", less),
+        ("@IMPORT a;", less),
+        ("@c: { a: true; }\n.m() when (@c [ a ] = true) {}", less),
+        (".a { b: ++1; }", less),
+        ("@import ur l(a.css);", less),
     ] {
         assert!(format(&allocator, source, options).is_err(), "{source:?} should fail to format");
     }