webapi: DOMTokenList-reflected attributes on area, output, iframe, link

Fixes 4 failing tests in WPT
/dom/lists/DOMTokenList-coverage-for-attributes.html (135/140 ->
139/140): area.relList, output.htmlFor, iframe.sandbox and link.sizes
must be DOMTokenList attributes reflecting their content attributes.

Element gains a generic getTokenList lookup (keyed by element and
attribute) alongside the existing class/rel dedicated ones, and the
four elements expose the accessors following the Anchor/Link relList
pattern (undefined outside the HTML namespace).

The remaining failure needs an SVGAElement interface (relList on SVG
<a> elements), which doesn't exist yet — SVG elements are all generic.

Coverage: /dom/lists/DOMTokenList-coverage-for-attributes.html
135/140 -> 139/140.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/browser/Frame.zig

@@ -134,6 +134,7 @@ _element_computed_styles: Element.StyleLookup = .empty,
 _element_datasets: Element.DatasetLookup = .empty,
 _element_class_lists: Element.ClassListLookup = .empty,
 _element_rel_lists: Element.RelListLookup = .empty,
+_element_token_lists: Element.TokenListLookup = .empty,
 _element_shadow_roots: Element.ShadowRootLookup = .empty,
 _node_owner_documents: Node.OwnerDocumentLookup = .empty,
 _element_scroll_positions: Element.ScrollPositionLookup = .empty,

src/browser/webapi/Element.zig

@@ -885,6 +885,23 @@ pub fn getRelList(self: *Element, frame: *Frame) !*collections.DOMTokenList {
     return gop.value_ptr.*;
 }
 
+// The other DOMTokenList-reflected attributes (class and rel have dedicated
+// lookups above).
+pub const TokenListAttribute = enum { sizes, sandbox, @"for" };
+pub const TokenListKey = struct { element: *Element, attribute: TokenListAttribute };
+pub const TokenListLookup = std.AutoHashMapUnmanaged(TokenListKey, *collections.DOMTokenList);
+
+pub fn getTokenList(self: *Element, comptime attribute: TokenListAttribute, frame: *Frame) !*collections.DOMTokenList {
+    const gop = try frame._element_token_lists.getOrPut(frame.arena, .{ .element = self, .attribute = attribute });
+    if (!gop.found_existing) {
+        gop.value_ptr.* = try frame._factory.create(collections.DOMTokenList{
+            ._element = self,
+            ._attribute_name = comptime .wrap(@tagName(attribute)),
+        });
+    }
+    return gop.value_ptr.*;
+}
+
 pub fn getDataset(self: *Element, frame: *Frame) !*DOMStringMap {
     const gop = try frame._element_datasets.getOrPut(frame.arena, self);
     if (!gop.found_existing) {

src/browser/webapi/element/html/Area.zig

@@ -290,12 +290,11 @@ pub const JsApi = struct {
     pub const referrerPolicy = bridge.accessor(Area.getReferrerPolicy, Area.setReferrerPolicy, .{ .ce_reactions = true });
     pub const relList = bridge.accessor(_getRelList, null, .{ .null_as_undefined = true });
     pub const toString = bridge.function(Area.getHref, .{});
-
+    pub const relList = bridge.accessor(_getRelList, null, .{ .null_as_undefined = true });
     fn _getRelList(self: *Area, frame: *Frame) !?*@import("../../collections.zig").DOMTokenList {
         const element = self.asElement();
-        // relList is only valid for HTML and SVG <area> elements
-        const namespace = element._namespace;
-        if (namespace != .html and namespace != .svg) {
+        // relList is only valid for HTML <area> elements
+        if (element._namespace != .html) {
             return null;
         }
         return element.getRelList(frame);

src/browser/webapi/element/html/IFrame.zig

@@ -93,6 +93,15 @@ pub const JsApi = struct {
     pub const name = bridge.accessor(IFrame.getName, IFrame.setName, .{ .ce_reactions = true });
     pub const contentWindow = bridge.accessor(IFrame.getContentWindow, null, .{});
     pub const contentDocument = bridge.accessor(IFrame.getContentDocument, null, .{});
+    pub const sandbox = bridge.accessor(_getSandbox, null, .{ .null_as_undefined = true });
+
+    fn _getSandbox(self: *IFrame, frame: *Frame) !?*@import("../../collections.zig").DOMTokenList {
+        const element = self.asElement();
+        if (element._namespace != .html) {
+            return null;
+        }
+        return element.getTokenList(.sandbox, frame);
+    }
 };
 
 pub const Build = struct {

src/browser/webapi/element/html/Link.zig

@@ -256,6 +256,15 @@ pub const JsApi = struct {
     pub const rev = bridge.accessor(Link.getRev, Link.setRev, .{ .ce_reactions = true });
     pub const target = bridge.accessor(Link.getTarget, Link.setTarget, .{ .ce_reactions = true });
     pub const relList = bridge.accessor(_getRelList, null, .{ .null_as_undefined = true });
+    pub const sizes = bridge.accessor(_getSizes, null, .{ .null_as_undefined = true });
+
+    fn _getSizes(self: *Link, frame: *Frame) !?*@import("../../collections.zig").DOMTokenList {
+        const element = self.asElement();
+        if (element._namespace != .html) {
+            return null;
+        }
+        return element.getTokenList(.sizes, frame);
+    }
 
     fn _getRelList(self: *Link, frame: *Frame) !?*@import("../../collections.zig").DOMTokenList {
         const element = self.asElement();

src/browser/webapi/element/html/Output.zig

@@ -29,4 +29,13 @@ pub const JsApi = struct {
     };
 
     pub const labels = bridge.accessor(Output.getLabels, null, .{});
+    pub const htmlFor = bridge.accessor(_getHtmlFor, null, .{ .null_as_undefined = true });
+
+    fn _getHtmlFor(self: *Output, frame: *Frame) !?*@import("../../collections.zig").DOMTokenList {
+        const element = self.asElement();
+        if (element._namespace != .html) {
+            return null;
+        }
+        return element.getTokenList(.@"for", frame);
+    }
 };