diff --git a/src/browser/Page.zig b/src/browser/Page.zig
index bf87fad7..5e4578c1 100644
--- a/src/browser/Page.zig
+++ b/src/browser/Page.zig
@@ -2490,13 +2490,16 @@ pub fn createCDATASection(self: *Page, data: []const u8) !*Node {
 }
 
 pub fn createProcessingInstruction(self: *Page, target: []const u8, data: []const u8) !*Node {
-    // Validate target doesn't contain "?>"
+    // Validate neither target nor data contain "?>"
     if (std.mem.indexOf(u8, target, "?>") != null) {
         return error.InvalidCharacterError;
     }
+    if (std.mem.indexOf(u8, data, "?>") != null) {
+        return error.InvalidCharacterError;
+    }
 
-    // Validate target follows XML name rules (similar to attribute name validation)
-    try Element.Attribute.validateAttributeName(.wrap(target));
+    // Validate target follows XML Name production
+    try validateXmlName(target);
 
     const owned_target = try self.dupeString(target);
     const owned_data = try self.dupeString(data);
@@ -2518,6 +2521,63 @@ pub fn createProcessingInstruction(self: *Page, target: []const u8, data: []cons
     return cd.asNode();
 }
 
+/// Validate a string against the XML Name production.
+/// https://www.w3.org/TR/xml/#NT-Name
+fn validateXmlName(name: []const u8) !void {
+    if (name.len == 0) return error.InvalidCharacterError;
+
+    var i: usize = 0;
+
+    // First character must be a NameStartChar.
+    const first_len = std.unicode.utf8ByteSequenceLength(name[0]) catch
+        return error.InvalidCharacterError;
+    if (first_len > name.len) return error.InvalidCharacterError;
+    const first_cp = std.unicode.utf8Decode(name[0..][0..first_len]) catch
+        return error.InvalidCharacterError;
+    if (!isXmlNameStartChar(first_cp)) return error.InvalidCharacterError;
+    i = first_len;
+
+    // Subsequent characters must be NameChars.
+    while (i < name.len) {
+        const cp_len = std.unicode.utf8ByteSequenceLength(name[i]) catch
+            return error.InvalidCharacterError;
+        if (i + cp_len > name.len) return error.InvalidCharacterError;
+        const cp = std.unicode.utf8Decode(name[i..][0..cp_len]) catch
+            return error.InvalidCharacterError;
+        if (!isXmlNameChar(cp)) return error.InvalidCharacterError;
+        i += cp_len;
+    }
+}
+
+fn isXmlNameStartChar(c: u21) bool {
+    return c == ':' or
+        (c >= 'A' and c <= 'Z') or
+        c == '_' or
+        (c >= 'a' and c <= 'z') or
+        (c >= 0xC0 and c <= 0xD6) or
+        (c >= 0xD8 and c <= 0xF6) or
+        (c >= 0xF8 and c <= 0x2FF) or
+        (c >= 0x370 and c <= 0x37D) or
+        (c >= 0x37F and c <= 0x1FFF) or
+        (c >= 0x200C and c <= 0x200D) or
+        (c >= 0x2070 and c <= 0x218F) or
+        (c >= 0x2C00 and c <= 0x2FEF) or
+        (c >= 0x3001 and c <= 0xD7FF) or
+        (c >= 0xF900 and c <= 0xFDCF) or
+        (c >= 0xFDF0 and c <= 0xFFFD) or
+        (c >= 0x10000 and c <= 0xEFFFF);
+}
+
+fn isXmlNameChar(c: u21) bool {
+    return isXmlNameStartChar(c) or
+        c == '-' or
+        c == '.' or
+        (c >= '0' and c <= '9') or
+        c == 0xB7 or
+        (c >= 0x300 and c <= 0x36F) or
+        (c >= 0x203F and c <= 0x2040);
+}
+
 pub fn dupeString(self: *Page, value: []const u8) ![]const u8 {
     if (String.intern(value)) |v| {
         return v;
diff --git a/src/browser/js/bridge.zig b/src/browser/js/bridge.zig
index 3a991313..46a7e235 100644
--- a/src/browser/js/bridge.zig
+++ b/src/browser/js/bridge.zig
@@ -713,6 +713,7 @@ pub const JsApis = flattenTypes(&.{
     @import("../webapi/css/CSSStyleRule.zig"),
     @import("../webapi/css/CSSStyleSheet.zig"),
     @import("../webapi/css/CSSStyleProperties.zig"),
+    @import("../webapi/css/FontFaceSet.zig"),
     @import("../webapi/css/MediaQueryList.zig"),
     @import("../webapi/css/StyleSheetList.zig"),
     @import("../webapi/Document.zig"),
@@ -865,6 +866,8 @@ pub const JsApis = flattenTypes(&.{
     @import("../webapi/navigation/NavigationActivation.zig"),
     @import("../webapi/canvas/CanvasRenderingContext2D.zig"),
     @import("../webapi/canvas/WebGLRenderingContext.zig"),
+    @import("../webapi/canvas/OffscreenCanvas.zig"),
+    @import("../webapi/canvas/OffscreenCanvasRenderingContext2D.zig"),
     @import("../webapi/SubtleCrypto.zig"),
     @import("../webapi/Selection.zig"),
     @import("../webapi/ImageData.zig"),
diff --git a/src/browser/tests/canvas/offscreen_canvas.html b/src/browser/tests/canvas/offscreen_canvas.html
new file mode 100644
index 00000000..f162213a
--- /dev/null
+++ b/src/browser/tests/canvas/offscreen_canvas.html
@@ -0,0 +1,64 @@
+<!DOCTYPE html>
+<script src="../testing.js"></script>
+
+<script id=OffscreenCanvas>
+{
+  const canvas = new OffscreenCanvas(256, 256);
+  testing.expectEqual(true, canvas instanceof OffscreenCanvas);
+  testing.expectEqual(canvas.width, 256);
+  testing.expectEqual(canvas.height, 256);
+}
+</script>
+
+<script id=OffscreenCanvas#width>
+{
+  const canvas = new OffscreenCanvas(100, 200);
+  testing.expectEqual(canvas.width, 100);
+  canvas.width = 300;
+  testing.expectEqual(canvas.width, 300);
+}
+</script>
+
+<script id=OffscreenCanvas#height>
+{
+  const canvas = new OffscreenCanvas(100, 200);
+  testing.expectEqual(canvas.height, 200);
+  canvas.height = 400;
+  testing.expectEqual(canvas.height, 400);
+}
+</script>
+
+<script id=OffscreenCanvas#getContext>
+{
+  const canvas = new OffscreenCanvas(64, 64);
+  const ctx = canvas.getContext("2d");
+  testing.expectEqual(true, ctx instanceof OffscreenCanvasRenderingContext2D);
+  // We can't really test rendering but let's try to call it at least.
+  ctx.fillRect(0, 0, 10, 10);
+}
+</script>
+
+<script id=OffscreenCanvas#convertToBlob>
+{
+  const canvas = new OffscreenCanvas(64, 64);
+  const promise = canvas.convertToBlob();
+  testing.expectEqual(true, promise instanceof Promise);
+  // The promise should resolve to a Blob (even if empty)
+  promise.then(blob => {
+    testing.expectEqual(true, blob instanceof Blob);
+    testing.expectEqual(blob.size, 0); // Empty since no rendering
+  });
+}
+</script>
+
+<script id=HTMLCanvasElement#transferControlToOffscreen>
+{
+  const htmlCanvas = document.createElement("canvas");
+  htmlCanvas.width = 128;
+  htmlCanvas.height = 96;
+  const offscreen = htmlCanvas.transferControlToOffscreen();
+  testing.expectEqual(true, offscreen instanceof OffscreenCanvas);
+  testing.expectEqual(offscreen.width, 128);
+  testing.expectEqual(offscreen.height, 96);
+}
+</script>
diff --git a/src/browser/tests/css/font_face_set.html b/src/browser/tests/css/font_face_set.html
new file mode 100644
index 00000000..a860669e
--- /dev/null
+++ b/src/browser/tests/css/font_face_set.html
@@ -0,0 +1,58 @@
+<!DOCTYPE html>
+<script src="../testing.js"></script>
+
+<script id="document_fonts_exists">
+{
+    testing.expectTrue(document.fonts !== undefined);
+    testing.expectTrue(document.fonts !== null);
+}
+</script>
+
+<script id="document_fonts_same_instance">
+{
+    // Should return same instance each time
+    const f1 = document.fonts;
+    const f2 = document.fonts;
+    testing.expectTrue(f1 === f2);
+}
+</script>
+
+<script id="document_fonts_status">
+{
+    testing.expectEqual('loaded', document.fonts.status);
+}
+</script>
+
+<script id="document_fonts_size">
+{
+    testing.expectEqual(0, document.fonts.size);
+}
+</script>
+
+<script id="document_fonts_ready_is_promise">
+{
+    const ready = document.fonts.ready;
+    testing.expectTrue(ready instanceof Promise);
+}
+</script>
+
+<script id="document_fonts_ready_resolves">
+{
+    let resolved = false;
+    document.fonts.ready.then(() => { resolved = true; });
+    // Promise resolution is async; just confirm .then() does not throw
+    testing.expectTrue(typeof document.fonts.ready.then === 'function');
+}
+</script>
+
+<script id="document_fonts_check">
+{
+    testing.expectTrue(document.fonts.check('16px sans-serif'));
+}
+</script>
+
+<script id="document_fonts_constructor_name">
+{
+    testing.expectEqual('FontFaceSet', document.fonts.constructor.name);
+}
+</script>
diff --git a/src/browser/tests/element/html/input.html b/src/browser/tests/element/html/input.html
index 8fab2b5a..2f8940cc 100644
--- a/src/browser/tests/element/html/input.html
+++ b/src/browser/tests/element/html/input.html
@@ -46,7 +46,7 @@
     testing.expectEqual(5, input.maxLength);
     input.maxLength = 'banana';
     testing.expectEqual(0, input.maxLength);
-    testing.expectError('Error: NegativeValueNotAllowed', () => { input.maxLength = -45;});
+    testing.expectError('IndexSizeError: Index or size is negative or greater than the allowed amount', () => { input.maxLength = -45;});
 
     testing.expectEqual(20, input.size);
     input.size = 5;
diff --git a/src/browser/tests/element/html/option.html b/src/browser/tests/element/html/option.html
index 6e7f72c8..45983370 100644
--- a/src/browser/tests/element/html/option.html
+++ b/src/browser/tests/element/html/option.html
@@ -29,6 +29,12 @@
   testing.expectEqual('Text 3', $('#opt3').text)
 </script>
 
+<script id="text_set">
+  $('#opt1').text = 'New Text 1'
+  testing.expectEqual('New Text 1', $('#opt1').text)
+  testing.expectEqual('New Text 1', $('#opt1').textContent)
+</script>
+
 <script id="selected">
   testing.expectEqual(false, $('#opt1').selected)
   testing.expectEqual(true, $('#opt2').selected)
diff --git a/src/browser/tests/legacy/html/input.html b/src/browser/tests/legacy/html/input.html
index 45963d81..0232ddbf 100644
--- a/src/browser/tests/legacy/html/input.html
+++ b/src/browser/tests/legacy/html/input.html
@@ -43,7 +43,7 @@
   testing.expectEqual(5, input.maxLength);
   input.maxLength = 'banana';
   testing.expectEqual(0, input.maxLength);
-  testing.expectError('Error: NegativeValueNotAllowed', () => { input.maxLength = -45;});
+  testing.expectError('IndexSizeError: Index or size is negative or greater than the allowed amount', () => { input.maxLength = -45;});
 
   testing.expectEqual(20, input.size);
   input.size = 5;
diff --git a/src/browser/webapi/Document.zig b/src/browser/webapi/Document.zig
index 4ee70ded..a5e75bd7 100644
--- a/src/browser/webapi/Document.zig
+++ b/src/browser/webapi/Document.zig
@@ -34,6 +34,7 @@ const DOMTreeWalker = @import("DOMTreeWalker.zig");
 const DOMNodeIterator = @import("DOMNodeIterator.zig");
 const DOMImplementation = @import("DOMImplementation.zig");
 const StyleSheetList = @import("css/StyleSheetList.zig");
+const FontFaceSet = @import("css/FontFaceSet.zig");
 const Selection = @import("Selection.zig");
 
 pub const XMLDocument = @import("XMLDocument.zig");
@@ -53,6 +54,7 @@ _removed_ids: std.StringHashMapUnmanaged(void) = .empty,
 _active_element: ?*Element = null,
 _style_sheets: ?*StyleSheetList = null,
 _implementation: ?*DOMImplementation = null,
+_fonts: ?*FontFaceSet = null,
 _write_insertion_point: ?*Node = null,
 _script_created_parser: ?Parser.Streaming = null,
 _adopted_style_sheets: ?js.Object.Global = null,
@@ -434,6 +436,15 @@ pub fn getStyleSheets(self: *Document, page: *Page) !*StyleSheetList {
     return sheets;
 }
 
+pub fn getFonts(self: *Document, page: *Page) !*FontFaceSet {
+    if (self._fonts) |fonts| {
+        return fonts;
+    }
+    const fonts = try FontFaceSet.init(page);
+    self._fonts = fonts;
+    return fonts;
+}
+
 pub fn adoptNode(_: *const Document, node: *Node, page: *Page) !*Node {
     if (node._type == .document) {
         return error.NotSupported;
@@ -968,6 +979,7 @@ pub const JsApi = struct {
     pub const implementation = bridge.accessor(Document.getImplementation, null, .{});
     pub const activeElement = bridge.accessor(Document.getActiveElement, null, .{});
     pub const styleSheets = bridge.accessor(Document.getStyleSheets, null, .{});
+    pub const fonts = bridge.accessor(Document.getFonts, null, .{});
     pub const contentType = bridge.accessor(Document.getContentType, null, .{});
     pub const domain = bridge.accessor(Document.getDomain, null, .{});
     pub const createElement = bridge.function(Document.createElement, .{ .dom_exception = true });
diff --git a/src/browser/webapi/Element.zig b/src/browser/webapi/Element.zig
index 753d50a7..f37be4da 100644
--- a/src/browser/webapi/Element.zig
+++ b/src/browser/webapi/Element.zig
@@ -1374,13 +1374,6 @@ fn upperTagName(tag_name: *String, buf: []u8) []const u8 {
         return tag_name.str();
     }
     const tag = tag_name.str();
-    // If the tag_name has a prefix, we must uppercase only the suffix part.
-    // example: te:st should be returned as te:ST.
-    if (std.mem.indexOfPos(u8, tag, 0, ":")) |pos| {
-        @memcpy(buf[0 .. pos + 1], tag[0 .. pos + 1]);
-        _ = std.ascii.upperString(buf[pos..tag.len], tag[pos..tag.len]);
-        return buf[0..tag.len];
-    }
     return std.ascii.upperString(buf, tag);
 }
 
diff --git a/src/browser/webapi/canvas/OffscreenCanvas.zig b/src/browser/webapi/canvas/OffscreenCanvas.zig
new file mode 100644
index 00000000..be83c146
--- /dev/null
+++ b/src/browser/webapi/canvas/OffscreenCanvas.zig
@@ -0,0 +1,105 @@
+// Copyright (C) 2023-2026  Lightpanda (Selecy SAS)
+//
+// Francis Bouvier <francis@lightpanda.io>
+// Pierre Tachoire <pierre@lightpanda.io>
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as
+// published by the Free Software Foundation, either version 3 of the
+// License, or (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+const std = @import("std");
+const js = @import("../../js/js.zig");
+const Page = @import("../../Page.zig");
+
+const Blob = @import("../Blob.zig");
+const OffscreenCanvasRenderingContext2D = @import("OffscreenCanvasRenderingContext2D.zig");
+
+/// https://developer.mozilla.org/en-US/docs/Web/API/OffscreenCanvas
+const OffscreenCanvas = @This();
+
+pub const _prototype_root = true;
+
+_width: u32,
+_height: u32,
+
+/// Since there's no base class rendering contextes inherit from,
+/// we're using tagged union.
+const DrawingContext = union(enum) {
+    @"2d": *OffscreenCanvasRenderingContext2D,
+};
+
+pub fn constructor(width: u32, height: u32, page: *Page) !*OffscreenCanvas {
+    return page._factory.create(OffscreenCanvas{
+        ._width = width,
+        ._height = height,
+    });
+}
+
+pub fn getWidth(self: *const OffscreenCanvas) u32 {
+    return self._width;
+}
+
+pub fn setWidth(self: *OffscreenCanvas, value: u32) void {
+    self._width = value;
+}
+
+pub fn getHeight(self: *const OffscreenCanvas) u32 {
+    return self._height;
+}
+
+pub fn setHeight(self: *OffscreenCanvas, value: u32) void {
+    self._height = value;
+}
+
+pub fn getContext(_: *OffscreenCanvas, context_type: []const u8, page: *Page) !?DrawingContext {
+    if (std.mem.eql(u8, context_type, "2d")) {
+        const ctx = try page._factory.create(OffscreenCanvasRenderingContext2D{});
+        return .{ .@"2d" = ctx };
+    }
+
+    return null;
+}
+
+/// Returns a Promise that resolves to a Blob containing the image.
+/// Since we have no actual rendering, this returns an empty blob.
+pub fn convertToBlob(_: *OffscreenCanvas, page: *Page) !js.Promise {
+    const blob = try Blob.init(null, null, page);
+    return page.js.local.?.resolvePromise(blob);
+}
+
+/// Returns an ImageBitmap with the rendered content (stub).
+pub fn transferToImageBitmap(_: *OffscreenCanvas) ?void {
+    // ImageBitmap not implemented yet, return null
+    return null;
+}
+
+pub const JsApi = struct {
+    pub const bridge = js.Bridge(OffscreenCanvas);
+
+    pub const Meta = struct {
+        pub const name = "OffscreenCanvas";
+        pub const prototype_chain = bridge.prototypeChain();
+        pub var class_id: bridge.ClassId = undefined;
+    };
+
+    pub const constructor = bridge.constructor(OffscreenCanvas.constructor, .{});
+    pub const width = bridge.accessor(OffscreenCanvas.getWidth, OffscreenCanvas.setWidth, .{});
+    pub const height = bridge.accessor(OffscreenCanvas.getHeight, OffscreenCanvas.setHeight, .{});
+    pub const getContext = bridge.function(OffscreenCanvas.getContext, .{});
+    pub const convertToBlob = bridge.function(OffscreenCanvas.convertToBlob, .{});
+    pub const transferToImageBitmap = bridge.function(OffscreenCanvas.transferToImageBitmap, .{});
+};
+
+const testing = @import("../../../testing.zig");
+test "WebApi: OffscreenCanvas" {
+    try testing.htmlRunner("canvas/offscreen_canvas.html", .{});
+}
diff --git a/src/browser/webapi/canvas/OffscreenCanvasRenderingContext2D.zig b/src/browser/webapi/canvas/OffscreenCanvasRenderingContext2D.zig
new file mode 100644
index 00000000..26ebb8ec
--- /dev/null
+++ b/src/browser/webapi/canvas/OffscreenCanvasRenderingContext2D.zig
@@ -0,0 +1,209 @@
+// Copyright (C) 2023-2025  Lightpanda (Selecy SAS)
+//
+// Francis Bouvier <francis@lightpanda.io>
+// Pierre Tachoire <pierre@lightpanda.io>
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as
+// published by the Free Software Foundation, either version 3 of the
+// License, or (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+const std = @import("std");
+
+const js = @import("../../js/js.zig");
+const color = @import("../../color.zig");
+const Page = @import("../../Page.zig");
+
+const ImageData = @import("../ImageData.zig");
+
+/// This class doesn't implement a `constructor`.
+/// It can be obtained with a call to `OffscreenCanvas#getContext`.
+/// https://developer.mozilla.org/en-US/docs/Web/API/OffscreenCanvasRenderingContext2D
+const OffscreenCanvasRenderingContext2D = @This();
+/// Fill color.
+/// TODO: Add support for `CanvasGradient` and `CanvasPattern`.
+_fill_style: color.RGBA = color.RGBA.Named.black,
+
+pub fn getFillStyle(self: *const OffscreenCanvasRenderingContext2D, page: *Page) ![]const u8 {
+    var w = std.Io.Writer.Allocating.init(page.call_arena);
+    try self._fill_style.format(&w.writer);
+    return w.written();
+}
+
+pub fn setFillStyle(
+    self: *OffscreenCanvasRenderingContext2D,
+    value: []const u8,
+) !void {
+    // Prefer the same fill_style if fails.
+    self._fill_style = color.RGBA.parse(value) catch self._fill_style;
+}
+
+pub fn getGlobalAlpha(_: *const OffscreenCanvasRenderingContext2D) f64 {
+    return 1.0;
+}
+
+pub fn getGlobalCompositeOperation(_: *const OffscreenCanvasRenderingContext2D) []const u8 {
+    return "source-over";
+}
+
+pub fn getStrokeStyle(_: *const OffscreenCanvasRenderingContext2D) []const u8 {
+    return "#000000";
+}
+
+pub fn getLineWidth(_: *const OffscreenCanvasRenderingContext2D) f64 {
+    return 1.0;
+}
+
+pub fn getLineCap(_: *const OffscreenCanvasRenderingContext2D) []const u8 {
+    return "butt";
+}
+
+pub fn getLineJoin(_: *const OffscreenCanvasRenderingContext2D) []const u8 {
+    return "miter";
+}
+
+pub fn getMiterLimit(_: *const OffscreenCanvasRenderingContext2D) f64 {
+    return 10.0;
+}
+
+pub fn getFont(_: *const OffscreenCanvasRenderingContext2D) []const u8 {
+    return "10px sans-serif";
+}
+
+pub fn getTextAlign(_: *const OffscreenCanvasRenderingContext2D) []const u8 {
+    return "start";
+}
+
+pub fn getTextBaseline(_: *const OffscreenCanvasRenderingContext2D) []const u8 {
+    return "alphabetic";
+}
+
+const WidthOrImageData = union(enum) {
+    width: u32,
+    image_data: *ImageData,
+};
+
+pub fn createImageData(
+    _: *const OffscreenCanvasRenderingContext2D,
+    width_or_image_data: WidthOrImageData,
+    /// If `ImageData` variant preferred, this is null.
+    maybe_height: ?u32,
+    /// Can be used if width and height provided.
+    maybe_settings: ?ImageData.ConstructorSettings,
+    page: *Page,
+) !*ImageData {
+    switch (width_or_image_data) {
+        .width => |width| {
+            const height = maybe_height orelse return error.TypeError;
+            return ImageData.constructor(width, height, maybe_settings, page);
+        },
+        .image_data => |image_data| {
+            return ImageData.constructor(image_data._width, image_data._height, null, page);
+        },
+    }
+}
+
+pub fn putImageData(_: *const OffscreenCanvasRenderingContext2D, _: *ImageData, _: f64, _: f64, _: ?f64, _: ?f64, _: ?f64, _: ?f64) void {}
+
+pub fn save(_: *OffscreenCanvasRenderingContext2D) void {}
+pub fn restore(_: *OffscreenCanvasRenderingContext2D) void {}
+pub fn scale(_: *OffscreenCanvasRenderingContext2D, _: f64, _: f64) void {}
+pub fn rotate(_: *OffscreenCanvasRenderingContext2D, _: f64) void {}
+pub fn translate(_: *OffscreenCanvasRenderingContext2D, _: f64, _: f64) void {}
+pub fn transform(_: *OffscreenCanvasRenderingContext2D, _: f64, _: f64, _: f64, _: f64, _: f64, _: f64) void {}
+pub fn setTransform(_: *OffscreenCanvasRenderingContext2D, _: f64, _: f64, _: f64, _: f64, _: f64, _: f64) void {}
+pub fn resetTransform(_: *OffscreenCanvasRenderingContext2D) void {}
+pub fn setGlobalAlpha(_: *OffscreenCanvasRenderingContext2D, _: f64) void {}
+pub fn setGlobalCompositeOperation(_: *OffscreenCanvasRenderingContext2D, _: []const u8) void {}
+pub fn setStrokeStyle(_: *OffscreenCanvasRenderingContext2D, _: []const u8) void {}
+pub fn setLineWidth(_: *OffscreenCanvasRenderingContext2D, _: f64) void {}
+pub fn setLineCap(_: *OffscreenCanvasRenderingContext2D, _: []const u8) void {}
+pub fn setLineJoin(_: *OffscreenCanvasRenderingContext2D, _: []const u8) void {}
+pub fn setMiterLimit(_: *OffscreenCanvasRenderingContext2D, _: f64) void {}
+pub fn clearRect(_: *OffscreenCanvasRenderingContext2D, _: f64, _: f64, _: f64, _: f64) void {}
+pub fn fillRect(_: *OffscreenCanvasRenderingContext2D, _: f64, _: f64, _: f64, _: f64) void {}
+pub fn strokeRect(_: *OffscreenCanvasRenderingContext2D, _: f64, _: f64, _: f64, _: f64) void {}
+pub fn beginPath(_: *OffscreenCanvasRenderingContext2D) void {}
+pub fn closePath(_: *OffscreenCanvasRenderingContext2D) void {}
+pub fn moveTo(_: *OffscreenCanvasRenderingContext2D, _: f64, _: f64) void {}
+pub fn lineTo(_: *OffscreenCanvasRenderingContext2D, _: f64, _: f64) void {}
+pub fn quadraticCurveTo(_: *OffscreenCanvasRenderingContext2D, _: f64, _: f64, _: f64, _: f64) void {}
+pub fn bezierCurveTo(_: *OffscreenCanvasRenderingContext2D, _: f64, _: f64, _: f64, _: f64, _: f64, _: f64) void {}
+pub fn arc(_: *OffscreenCanvasRenderingContext2D, _: f64, _: f64, _: f64, _: f64, _: f64, _: ?bool) void {}
+pub fn arcTo(_: *OffscreenCanvasRenderingContext2D, _: f64, _: f64, _: f64, _: f64, _: f64) void {}
+pub fn rect(_: *OffscreenCanvasRenderingContext2D, _: f64, _: f64, _: f64, _: f64) void {}
+pub fn fill(_: *OffscreenCanvasRenderingContext2D) void {}
+pub fn stroke(_: *OffscreenCanvasRenderingContext2D) void {}
+pub fn clip(_: *OffscreenCanvasRenderingContext2D) void {}
+pub fn setFont(_: *OffscreenCanvasRenderingContext2D, _: []const u8) void {}
+pub fn setTextAlign(_: *OffscreenCanvasRenderingContext2D, _: []const u8) void {}
+pub fn setTextBaseline(_: *OffscreenCanvasRenderingContext2D, _: []const u8) void {}
+pub fn fillText(_: *OffscreenCanvasRenderingContext2D, _: []const u8, _: f64, _: f64, _: ?f64) void {}
+pub fn strokeText(_: *OffscreenCanvasRenderingContext2D, _: []const u8, _: f64, _: f64, _: ?f64) void {}
+
+pub const JsApi = struct {
+    pub const bridge = js.Bridge(OffscreenCanvasRenderingContext2D);
+
+    pub const Meta = struct {
+        pub const name = "OffscreenCanvasRenderingContext2D";
+
+        pub const prototype_chain = bridge.prototypeChain();
+        pub var class_id: bridge.ClassId = undefined;
+    };
+
+    pub const createImageData = bridge.function(OffscreenCanvasRenderingContext2D.createImageData, .{ .dom_exception = true });
+    pub const putImageData = bridge.function(OffscreenCanvasRenderingContext2D.putImageData, .{});
+
+    pub const save = bridge.function(OffscreenCanvasRenderingContext2D.save, .{});
+    pub const restore = bridge.function(OffscreenCanvasRenderingContext2D.restore, .{});
+
+    pub const scale = bridge.function(OffscreenCanvasRenderingContext2D.scale, .{});
+    pub const rotate = bridge.function(OffscreenCanvasRenderingContext2D.rotate, .{});
+    pub const translate = bridge.function(OffscreenCanvasRenderingContext2D.translate, .{});
+    pub const transform = bridge.function(OffscreenCanvasRenderingContext2D.transform, .{});
+    pub const setTransform = bridge.function(OffscreenCanvasRenderingContext2D.setTransform, .{});
+    pub const resetTransform = bridge.function(OffscreenCanvasRenderingContext2D.resetTransform, .{});
+
+    pub const globalAlpha = bridge.accessor(OffscreenCanvasRenderingContext2D.getGlobalAlpha, OffscreenCanvasRenderingContext2D.setGlobalAlpha, .{});
+    pub const globalCompositeOperation = bridge.accessor(OffscreenCanvasRenderingContext2D.getGlobalCompositeOperation, OffscreenCanvasRenderingContext2D.setGlobalCompositeOperation, .{});
+
+    pub const fillStyle = bridge.accessor(OffscreenCanvasRenderingContext2D.getFillStyle, OffscreenCanvasRenderingContext2D.setFillStyle, .{});
+    pub const strokeStyle = bridge.accessor(OffscreenCanvasRenderingContext2D.getStrokeStyle, OffscreenCanvasRenderingContext2D.setStrokeStyle, .{});
+
+    pub const lineWidth = bridge.accessor(OffscreenCanvasRenderingContext2D.getLineWidth, OffscreenCanvasRenderingContext2D.setLineWidth, .{});
+    pub const lineCap = bridge.accessor(OffscreenCanvasRenderingContext2D.getLineCap, OffscreenCanvasRenderingContext2D.setLineCap, .{});
+    pub const lineJoin = bridge.accessor(OffscreenCanvasRenderingContext2D.getLineJoin, OffscreenCanvasRenderingContext2D.setLineJoin, .{});
+    pub const miterLimit = bridge.accessor(OffscreenCanvasRenderingContext2D.getMiterLimit, OffscreenCanvasRenderingContext2D.setMiterLimit, .{});
+
+    pub const clearRect = bridge.function(OffscreenCanvasRenderingContext2D.clearRect, .{});
+    pub const fillRect = bridge.function(OffscreenCanvasRenderingContext2D.fillRect, .{});
+    pub const strokeRect = bridge.function(OffscreenCanvasRenderingContext2D.strokeRect, .{});
+
+    pub const beginPath = bridge.function(OffscreenCanvasRenderingContext2D.beginPath, .{});
+    pub const closePath = bridge.function(OffscreenCanvasRenderingContext2D.closePath, .{});
+    pub const moveTo = bridge.function(OffscreenCanvasRenderingContext2D.moveTo, .{});
+    pub const lineTo = bridge.function(OffscreenCanvasRenderingContext2D.lineTo, .{});
+    pub const quadraticCurveTo = bridge.function(OffscreenCanvasRenderingContext2D.quadraticCurveTo, .{});
+    pub const bezierCurveTo = bridge.function(OffscreenCanvasRenderingContext2D.bezierCurveTo, .{});
+    pub const arc = bridge.function(OffscreenCanvasRenderingContext2D.arc, .{});
+    pub const arcTo = bridge.function(OffscreenCanvasRenderingContext2D.arcTo, .{});
+    pub const rect = bridge.function(OffscreenCanvasRenderingContext2D.rect, .{});
+
+    pub const fill = bridge.function(OffscreenCanvasRenderingContext2D.fill, .{});
+    pub const stroke = bridge.function(OffscreenCanvasRenderingContext2D.stroke, .{});
+    pub const clip = bridge.function(OffscreenCanvasRenderingContext2D.clip, .{});
+
+    pub const font = bridge.accessor(OffscreenCanvasRenderingContext2D.getFont, OffscreenCanvasRenderingContext2D.setFont, .{});
+    pub const textAlign = bridge.accessor(OffscreenCanvasRenderingContext2D.getTextAlign, OffscreenCanvasRenderingContext2D.setTextAlign, .{});
+    pub const textBaseline = bridge.accessor(OffscreenCanvasRenderingContext2D.getTextBaseline, OffscreenCanvasRenderingContext2D.setTextBaseline, .{});
+    pub const fillText = bridge.function(OffscreenCanvasRenderingContext2D.fillText, .{});
+    pub const strokeText = bridge.function(OffscreenCanvasRenderingContext2D.strokeText, .{});
+};
diff --git a/src/browser/webapi/css/FontFaceSet.zig b/src/browser/webapi/css/FontFaceSet.zig
new file mode 100644
index 00000000..cd3cf2b1
--- /dev/null
+++ b/src/browser/webapi/css/FontFaceSet.zig
@@ -0,0 +1,59 @@
+const std = @import("std");
+const js = @import("../../js/js.zig");
+const Page = @import("../../Page.zig");
+
+const FontFaceSet = @This();
+
+// Padding to avoid zero-size struct, which causes identity_map pointer collisions.
+_pad: bool = false,
+
+pub fn init(page: *Page) !*FontFaceSet {
+    return page._factory.create(FontFaceSet{});
+}
+
+// FontFaceSet.ready - returns an already-resolved Promise.
+// In a headless browser there is no font loading, so fonts are always ready.
+pub fn getReady(_: *FontFaceSet, page: *Page) !js.Promise {
+    return page.js.local.?.resolvePromise({});
+}
+
+pub fn getStatus(_: *const FontFaceSet) []const u8 {
+    return "loaded";
+}
+
+pub fn getSize(_: *const FontFaceSet) u32 {
+    return 0;
+}
+
+// check(font, text?) - always true; headless has no real fonts to check.
+pub fn check(_: *const FontFaceSet, font: []const u8) bool {
+    _ = font;
+    return true;
+}
+
+// load(font, text?) - resolves immediately with an empty array.
+pub fn load(_: *FontFaceSet, font: []const u8, page: *Page) !js.Promise {
+    _ = font;
+    return page.js.local.?.resolvePromise({});
+}
+
+pub const JsApi = struct {
+    pub const bridge = js.Bridge(FontFaceSet);
+
+    pub const Meta = struct {
+        pub const name = "FontFaceSet";
+        pub const prototype_chain = bridge.prototypeChain();
+        pub var class_id: bridge.ClassId = undefined;
+    };
+
+    pub const ready = bridge.accessor(FontFaceSet.getReady, null, .{});
+    pub const status = bridge.accessor(FontFaceSet.getStatus, null, .{});
+    pub const size = bridge.accessor(FontFaceSet.getSize, null, .{});
+    pub const check = bridge.function(FontFaceSet.check, .{});
+    pub const load = bridge.function(FontFaceSet.load, .{});
+};
+
+const testing = @import("../../../testing.zig");
+test "WebApi: FontFaceSet" {
+    try testing.htmlRunner("css/font_face_set.html", .{});
+}
diff --git a/src/browser/webapi/element/html/Canvas.zig b/src/browser/webapi/element/html/Canvas.zig
index 122552b5..a29dce4a 100644
--- a/src/browser/webapi/element/html/Canvas.zig
+++ b/src/browser/webapi/element/html/Canvas.zig
@@ -25,6 +25,7 @@ const HtmlElement = @import("../Html.zig");
 
 const CanvasRenderingContext2D = @import("../../canvas/CanvasRenderingContext2D.zig");
 const WebGLRenderingContext = @import("../../canvas/WebGLRenderingContext.zig");
+const OffscreenCanvas = @import("../../canvas/OffscreenCanvas.zig");
 
 const Canvas = @This();
 _proto: *HtmlElement,
@@ -80,6 +81,14 @@ pub fn getContext(_: *Canvas, context_type: []const u8, page: *Page) !?DrawingCo
     return null;
 }
 
+/// Transfers control of the canvas to an OffscreenCanvas.
+/// Returns an OffscreenCanvas with the same dimensions.
+pub fn transferControlToOffscreen(self: *Canvas, page: *Page) !*OffscreenCanvas {
+    const width = self.getWidth();
+    const height = self.getHeight();
+    return OffscreenCanvas.constructor(width, height, page);
+}
+
 pub const JsApi = struct {
     pub const bridge = js.Bridge(Canvas);
 
@@ -92,4 +101,5 @@ pub const JsApi = struct {
     pub const width = bridge.accessor(Canvas.getWidth, Canvas.setWidth, .{});
     pub const height = bridge.accessor(Canvas.getHeight, Canvas.setHeight, .{});
     pub const getContext = bridge.function(Canvas.getContext, .{});
+    pub const transferControlToOffscreen = bridge.function(Canvas.transferControlToOffscreen, .{});
 };
diff --git a/src/browser/webapi/element/html/Input.zig b/src/browser/webapi/element/html/Input.zig
index 831c5383..94f5d092 100644
--- a/src/browser/webapi/element/html/Input.zig
+++ b/src/browser/webapi/element/html/Input.zig
@@ -184,6 +184,26 @@ pub fn setDefaultChecked(self: *Input, checked: bool, page: *Page) !void {
     }
 }
 
+pub fn getWillValidate(self: *const Input) bool {
+    // An input element is barred from constraint validation if:
+    // - type is hidden, button, or reset
+    // - element is disabled
+    // - element has a datalist ancestor
+    return switch (self._input_type) {
+        .hidden, .button, .reset => false,
+        else => !self.getDisabled() and !self.hasDatalistAncestor(),
+    };
+}
+
+fn hasDatalistAncestor(self: *const Input) bool {
+    var node = self.asConstElement().asConstNode().parentElement();
+    while (node) |parent| {
+        if (parent.is(HtmlElement.DataList) != null) return true;
+        node = parent.asConstNode().parentElement();
+    }
+    return false;
+}
+
 pub fn getDisabled(self: *const Input) bool {
     // TODO: Also check for disabled fieldset ancestors
     // (but not if we're inside a <legend> of that fieldset)
@@ -229,7 +249,7 @@ pub fn getMaxLength(self: *const Input) i32 {
 
 pub fn setMaxLength(self: *Input, max_length: i32, page: *Page) !void {
     if (max_length < 0) {
-        return error.NegativeValueNotAllowed;
+        return error.IndexSizeError;
     }
     var buf: [32]u8 = undefined;
     const value = std.fmt.bufPrint(&buf, "{d}", .{max_length}) catch unreachable;
@@ -868,7 +888,7 @@ pub const JsApi = struct {
     pub const accept = bridge.accessor(Input.getAccept, Input.setAccept, .{});
     pub const readOnly = bridge.accessor(Input.getReadonly, Input.setReadonly, .{});
     pub const alt = bridge.accessor(Input.getAlt, Input.setAlt, .{});
-    pub const maxLength = bridge.accessor(Input.getMaxLength, Input.setMaxLength, .{});
+    pub const maxLength = bridge.accessor(Input.getMaxLength, Input.setMaxLength, .{ .dom_exception = true });
     pub const size = bridge.accessor(Input.getSize, Input.setSize, .{});
     pub const src = bridge.accessor(Input.getSrc, Input.setSrc, .{});
     pub const form = bridge.accessor(Input.getForm, null, .{});
@@ -879,6 +899,7 @@ pub const JsApi = struct {
     pub const step = bridge.accessor(Input.getStep, Input.setStep, .{});
     pub const multiple = bridge.accessor(Input.getMultiple, Input.setMultiple, .{});
     pub const autocomplete = bridge.accessor(Input.getAutocomplete, Input.setAutocomplete, .{});
+    pub const willValidate = bridge.accessor(Input.getWillValidate, null, .{});
     pub const select = bridge.function(Input.select, .{});
 
     pub const selectionStart = bridge.accessor(Input.getSelectionStart, Input.setSelectionStart, .{});
diff --git a/src/browser/webapi/element/html/Option.zig b/src/browser/webapi/element/html/Option.zig
index 023b04e0..c93e6820 100644
--- a/src/browser/webapi/element/html/Option.zig
+++ b/src/browser/webapi/element/html/Option.zig
@@ -67,6 +67,10 @@ pub fn getText(self: *const Option) []const u8 {
     return node.getTextContentAlloc(allocator) catch "";
 }
 
+pub fn setText(self: *Option, value: []const u8, page: *Page) !void {
+    try self.asNode().setTextContent(value, page);
+}
+
 pub fn getSelected(self: *const Option) bool {
     return self._selected;
 }
@@ -113,7 +117,7 @@ pub const JsApi = struct {
     };
 
     pub const value = bridge.accessor(Option.getValue, Option.setValue, .{});
-    pub const text = bridge.accessor(Option.getText, null, .{});
+    pub const text = bridge.accessor(Option.getText, Option.setText, .{});
     pub const selected = bridge.accessor(Option.getSelected, Option.setSelected, .{});
     pub const defaultSelected = bridge.accessor(Option.getDefaultSelected, null, .{});
     pub const disabled = bridge.accessor(Option.getDisabled, Option.setDisabled, .{});
diff --git a/src/browser/webapi/storage/Cookie.zig b/src/browser/webapi/storage/Cookie.zig
index 5e352bd4..da499efb 100644
--- a/src/browser/webapi/storage/Cookie.zig
+++ b/src/browser/webapi/storage/Cookie.zig
@@ -435,7 +435,7 @@ pub const Jar = struct {
     pub fn removeExpired(self: *Jar, request_time: ?i64) void {
         if (self.cookies.items.len == 0) return;
         const time = request_time orelse std.time.timestamp();
-        var i: usize = self.cookies.items.len ;
+        var i: usize = self.cookies.items.len;
         while (i > 0) {
             i -= 1;
             const cookie = &self.cookies.items[i];