diff --git a/src/browser/actions.zig b/src/browser/actions.zig
index 19a51d70f..40d66d523 100644
--- a/src/browser/actions.zig
+++ b/src/browser/actions.zig
@@ -46,7 +46,7 @@ fn dispatch(el: *Element, event: *Event, comptime typ: []const u8, frame: *Frame
     };
 }
 
-// Dispatches a trusted pointer event and reports whether it was cancelled.
+/// Dispatches a trusted pointer event and reports whether it was cancelled.
 fn dispatchPointer(el: *Element, comptime typ: []const u8, buttons: u16, detail: u32, frame: *Frame) !bool {
     const event: *PointerEvent = try .initTrusted(typ, .{
         .bubbles = true,
@@ -70,7 +70,7 @@ fn dispatchPointer(el: *Element, comptime typ: []const u8, buttons: u16, detail:
     return base_event.getDefaultPrevented();
 }
 
-fn dispatchMouse(el: *Element, comptime typ: []const u8, buttons: u16, frame: *Frame) !void {
+fn dispatchMouse(el: *Element, comptime typ: []const u8, buttons: u16, frame: *Frame) !bool {
     const event: *MouseEvent = try .initTrusted(comptime .wrap(typ), .{
         .bubbles = true,
         .cancelable = true,
@@ -78,7 +78,13 @@ fn dispatchMouse(el: *Element, comptime typ: []const u8, buttons: u16, frame: *F
         .buttons = buttons,
         .detail = 1,
     }, frame);
-    try dispatch(el, event.asEvent(), typ, frame);
+
+    const base_event = event.asEvent();
+    base_event.acquireRef();
+    defer base_event.releaseRef(frame._page);
+
+    try dispatch(el, base_event, typ, frame);
+    return base_event.getDefaultPrevented();
 }
 
 /// A full trusted primary-button click sequence, as a real user click would
@@ -97,15 +103,17 @@ pub fn click(node: *DOMNode, frame: *Frame) !void {
     // still fires.
     const suppress_mouse = try dispatchPointer(el, "pointerdown", 1, 0, frame);
     if (!suppress_mouse) {
-        try dispatchMouse(el, "mousedown", 1, frame);
-        Frame.user_input.focusForMouseDown(frame, el) catch |err| {
-            lp.log.warn(.app, "click mousedown focus", .{ .err = err });
-        };
+        const suppress_focus = try dispatchMouse(el, "mousedown", 1, frame);
+        if (!suppress_focus) {
+            Frame.user_input.focusForMouseDown(frame, el) catch |err| {
+                lp.log.warn(.app, "click mousedown focus", .{ .err = err });
+            };
+        }
     }
 
     _ = try dispatchPointer(el, "pointerup", 0, 0, frame);
     if (!suppress_mouse) {
-        try dispatchMouse(el, "mouseup", 0, frame);
+        _ = try dispatchMouse(el, "mouseup", 0, frame);
     }
 
     _ = try dispatchPointer(el, "click", 0, 1, frame);
diff --git a/src/browser/frame/user_input.zig b/src/browser/frame/user_input.zig
index 2bffc7347..6a3121b5f 100644
--- a/src/browser/frame/user_input.zig
+++ b/src/browser/frame/user_input.zig
@@ -180,10 +180,11 @@ fn dispatchBoundaryEvent(frame: *Frame, target: *Element, comptime mouse_typ: []
     };
 }
 
-// Dispatch a single trusted mouse event of the given type on `target`, carrying
-// the pressed button and pointer position. `detail` is the click count (used for
-// click/dblclick); 0 for events where it does not apply.
-fn dispatchMouseEventOn(frame: *Frame, target: *Element, comptime typ: []const u8, x: f64, y: f64, button: i32, detail: u32) !void {
+/// Dispatch a single trusted mouse event of the given type on `target`, carrying
+/// the pressed button and pointer position. `detail` is the click count (used for
+/// click/dblclick); 0 for events where it does not apply. Reports whether the
+/// event was cancelled via preventDefault().
+fn dispatchMouseEventOn(frame: *Frame, target: *Element, comptime typ: []const u8, x: f64, y: f64, button: i32, detail: u32) !bool {
     const event: *MouseEvent = try .initTrusted(comptime .wrap(typ), .{
         .bubbles = true,
         .cancelable = true,
@@ -193,7 +194,13 @@ fn dispatchMouseEventOn(frame: *Frame, target: *Element, comptime typ: []const u
         .button = button,
         .detail = detail,
     }, frame);
-    try frame._event_manager.dispatch(target.asEventTarget(), event.asEvent());
+
+    const base_event = event.asEvent();
+    base_event.acquireRef();
+    defer base_event.releaseRef(frame._page);
+
+    try frame._event_manager.dispatch(target.asEventTarget(), base_event);
+    return base_event.getDefaultPrevented();
 }
 
 pub fn triggerMousePress(frame: *Frame, x: f64, y: f64, button: i32) !void {
@@ -208,8 +215,10 @@ pub fn triggerMousePress(frame: *Frame, x: f64, y: f64, button: i32) !void {
             .type = frame._type,
         });
     }
-    try dispatchMouseEventOn(frame, target, "mousedown", x, y, button, 0);
-    try focusForMouseDown(frame, target);
+    const suppressed = try dispatchMouseEventOn(frame, target, "mousedown", x, y, button, 0);
+    if (!suppressed) {
+        try focusForMouseDown(frame, target);
+    }
 }
 
 pub fn triggerMouseMove(frame: *Frame, x: f64, y: f64) !void {
@@ -251,19 +260,19 @@ pub fn triggerMouseRelease(frame: *Frame, x: f64, y: f64, button: i32, click_cou
 
     const detail: u32 = if (click_count > 0) @intCast(click_count) else 1;
 
-    try dispatchMouseEventOn(frame, target, "mouseup", x, y, button, detail);
+    _ = try dispatchMouseEventOn(frame, target, "mouseup", x, y, button, detail);
 
     // After mouseup, the activation event depends on the button.
     switch (button) {
         mouse_button.main => {
-            try dispatchMouseEventOn(frame, target, "click", x, y, button, detail);
+            _ = try dispatchMouseEventOn(frame, target, "click", x, y, button, detail);
             // A second click in quick succession also fires dblclick.
             if (click_count == 2) {
-                try dispatchMouseEventOn(frame, target, "dblclick", x, y, button, detail);
+                _ = try dispatchMouseEventOn(frame, target, "dblclick", x, y, button, detail);
             }
         },
-        mouse_button.auxiliary => try dispatchMouseEventOn(frame, target, "auxclick", x, y, button, detail),
-        mouse_button.secondary => try dispatchMouseEventOn(frame, target, "contextmenu", x, y, button, detail),
+        mouse_button.auxiliary => _ = try dispatchMouseEventOn(frame, target, "auxclick", x, y, button, detail),
+        mouse_button.secondary => _ = try dispatchMouseEventOn(frame, target, "contextmenu", x, y, button, detail),
         else => {},
     }
 }
@@ -353,8 +362,8 @@ fn isEditingHost(node: *Node) bool {
     return std.ascii.eqlIgnoreCase(value, "false") == false;
 }
 
-// Find the outermost element of the contiguous editable chain containing the
-// target.
+/// Find the outermost element of the contiguous editable chain containing the
+/// target.
 fn outermostEditingHost(target: *Element) ?*Element {
     var node: ?*Node = target.asNode();
     var editable: ?*Node = null;
@@ -374,31 +383,42 @@ fn outermostEditingHost(target: *Element) ?*Element {
     return host.is(Element);
 }
 
-/// `null` means the element is not mouse-focusable. Unlike sequential focus,
-/// any explicit tabindex value, including a negative one, is mouse-focusable.
-fn mouseFocusTabIndex(el: *Element) ?i32 {
-    if (el.isDisabled()) return null;
-    if (el.is(Element.Html) == null) return null;
+/// Unlike sequential focus, any explicit, parseable tabindex value, including
+/// a negative one, is mouse-focusable — on any element, not just HTML ones, so
+/// this is checked before the HTML-only guard below. An unparsable tabindex is
+/// treated as if the attribute were absent (HTML §6.6.3), so native
+/// focusability still applies — mirrors HtmlElement.getTabIndex's
+/// parse-failure fallthrough.
+fn isMouseFocusable(el: *Element) bool {
+    if (el.isDisabled()) return false;
 
     if (el.getAttributeSafe(comptime .wrap("tabindex"))) |attr| {
-        return Element.Html.parseInteger(attr) orelse 0;
+        if (Element.Html.parseInteger(attr)) |_| {
+            return true;
+        }
     }
 
-    const native = switch (el.getTag()) {
+    if (el.is(Element.Html) == null) {
+        // Mirrors hasClickActivationBehavior: an SVG link is focusable by the
+        // same href it activates on.
+        if (el.is(Element.Svg.Graphics.A) != null) {
+            return svgAnchorHref(el) != null;
+        }
+        return false;
+    }
+
+    return switch (el.getTag()) {
         .button, .select, .textarea, .iframe => true,
         .input => el.as(Element.Html.Input)._input_type != .hidden,
         .anchor, .area => el.getAttributeSafe(comptime .wrap("href")) != null,
         else => false,
     };
-    return if (native) 0 else null;
-}
-
-fn isMouseFocusable(el: *Element) bool {
-    return mouseFocusTabIndex(el) != null;
 }
 
 /// Mousedown default action: focus the editing host if the click is inside
-/// one, otherwise the nearest mouse-focusable element (self or ancestor).
+/// one, otherwise the nearest mouse-focusable element (self or ancestor). If
+/// no ancestor is mouse-focusable, blur whatever was previously focused —
+/// a mousedown outside any focusable element moves focus to the body.
 pub fn focusForMouseDown(frame: *Frame, target: *Element) !void {
     if (outermostEditingHost(target)) |host| {
         try host.focus(frame);
@@ -413,6 +433,11 @@ pub fn focusForMouseDown(frame: *Frame, target: *Element) !void {
             return;
         }
     }
+
+    const doc = target.asNode().ownerDocument(frame) orelse frame.document;
+    if (doc._active_element) |active| {
+        try active.blur(frame);
+    }
 }
 
 // Per the DOM dispatch algorithm, a click's activation target is the event
diff --git a/src/browser/tests/mcp_actions.html b/src/browser/tests/mcp_actions.html
index 377d39395..2bab8999f 100644
--- a/src/browser/tests/mcp_actions.html
+++ b/src/browser/tests/mcp_actions.html
@@ -22,7 +22,7 @@
     <button id="btnPreventDefault">Prevent Default</button>
     <button id="btnDisabled" disabled>Disabled</button>
     <div id="focusTarget" tabindex="0" onclick="window.focusTargetFocused = document.activeElement === this;">Focus me</div>
-    <div id="plain" onclick="window.focusAfterPlain = document.activeElement.id;">Not focusable</div>
+    <div id="plain" onclick="window.plainBlurred = document.activeElement === document.body;">Not focusable</div>
     <script>
         window.seq = [];
         const btn = document.getElementById('btn');
@@ -39,8 +39,11 @@
             btnPreventDefault.addEventListener(t, function(e) { window.seqPrevented.push(e.type); });
         }
 
-        window.disabledMousedowned = false;
-        document.getElementById('btnDisabled').addEventListener('mousedown', function() { window.disabledMousedowned = true; });
+        window.disabledEvents = [];
+        const btnDisabled = document.getElementById('btnDisabled');
+        for (const t of ['pointerdown', 'mousedown', 'pointerup', 'mouseup', 'click']) {
+            btnDisabled.addEventListener(t, function(e) { window.disabledEvents.push(e.type); });
+        }
 
         document.getElementById('chk').addEventListener('click', function() { window.chkClicked = true; });
         document.getElementById('chk').addEventListener('change', function() { window.chkChanged = true; });
diff --git a/src/browser/webapi/WebDriver.zig b/src/browser/webapi/WebDriver.zig
index 6ddcb3aed..5f7d2ae3e 100644
--- a/src/browser/webapi/WebDriver.zig
+++ b/src/browser/webapi/WebDriver.zig
@@ -74,10 +74,10 @@ pub fn click(_: *const WebDriver, element: *Element, frame: *Frame) !void {
     }
 
     dispatchPointer(element, "pointerdown", 0, 1, frame);
-    dispatchMouse(element, "mousedown", 0, 1, 1, frame);
+    _ = dispatchMouse(element, "mousedown", 0, 1, 1, frame);
     dispatchPointer(element, "pointerup", 0, 0, frame);
-    dispatchMouse(element, "mouseup", 0, 0, 1, frame);
-    dispatchMouse(element, "click", 0, 0, 1, frame);
+    _ = dispatchMouse(element, "mouseup", 0, 0, 1, frame);
+    _ = dispatchMouse(element, "click", 0, 0, 1, frame);
 }
 
 const WebDriverCookie = struct {
@@ -281,7 +281,7 @@ fn performPointerSource(source: js.Object, frame: *Frame) !void {
                     .with_pointer = true,
                 });
                 dispatchPointer(el, "pointermove", 0, pressed_mask, frame);
-                dispatchMouse(el, "mousemove", 0, pressed_mask, 0, frame);
+                _ = dispatchMouse(el, "mousemove", 0, pressed_mask, 0, frame);
             }
         } else if (action_type.eql(comptime .wrap("pointerDown"))) {
             const el = target orelse continue;
@@ -298,10 +298,12 @@ fn performPointerSource(source: js.Object, frame: *Frame) !void {
             if (is_touch) {
                 dispatchTouch(el, "touchstart", frame);
             } else {
-                dispatchMouse(el, "mousedown", button, buttonsMask(button), click_count, frame);
-                Frame.user_input.focusForMouseDown(frame, el) catch |err| {
-                    log.warn(.app, "webdriver mousedown focus", .{ .err = err });
-                };
+                const suppressed = dispatchMouse(el, "mousedown", button, buttonsMask(button), click_count, frame);
+                if (!suppressed) {
+                    Frame.user_input.focusForMouseDown(frame, el) catch |err| {
+                        log.warn(.app, "webdriver mousedown focus", .{ .err = err });
+                    };
+                }
             }
         } else if (action_type.eql(comptime .wrap("pointerUp"))) {
             const el = target orelse continue;
@@ -312,20 +314,20 @@ fn performPointerSource(source: js.Object, frame: *Frame) !void {
             if (is_touch) {
                 dispatchTouch(el, "touchend", frame);
             } else {
-                dispatchMouse(el, "mouseup", button, 0, click_count, frame);
+                _ = dispatchMouse(el, "mouseup", button, 0, click_count, frame);
                 const click_target = commonClickTarget(down_target orelse el, el);
                 last_click_button = button;
                 last_click_target = click_target;
                 if (button == 0) {
-                    dispatchMouse(click_target, "click", button, 0, click_count, frame);
+                    _ = dispatchMouse(click_target, "click", button, 0, click_count, frame);
                     if (click_count % 2 == 0) {
-                        dispatchMouse(click_target, "dblclick", button, 0, click_count, frame);
+                        _ = dispatchMouse(click_target, "dblclick", button, 0, click_count, frame);
                     }
                 } else {
                     if (button == 2) {
-                        dispatchMouse(click_target, "contextmenu", button, 0, click_count, frame);
+                        _ = dispatchMouse(click_target, "contextmenu", button, 0, click_count, frame);
                     }
-                    dispatchMouse(click_target, "auxclick", button, 0, click_count, frame);
+                    _ = dispatchMouse(click_target, "auxclick", button, 0, click_count, frame);
                 }
             }
             down_target = null;
@@ -566,7 +568,7 @@ fn dispatchPointer(el: *Element, comptime typ: []const u8, button: i32, buttons:
     dispatch(el.asEventTarget(), event.asEvent(), frame, typ);
 }
 
-fn dispatchMouse(el: *Element, comptime typ: []const u8, button: i32, buttons: u16, detail: u32, frame: *Frame) void {
+fn dispatchMouse(el: *Element, comptime typ: []const u8, button: i32, buttons: u16, detail: u32, frame: *Frame) bool {
     const modifiers = frame._page.input_modifiers;
     const event = MouseEvent.initTrusted(comptime .wrap(typ), .{
         .bubbles = true,
@@ -581,9 +583,14 @@ fn dispatchMouse(el: *Element, comptime typ: []const u8, button: i32, buttons: u
         .metaKey = modifiers.meta,
     }, frame) catch |err| {
         log.warn(.app, "webdriver mouse event", .{ .err = err, .type = typ });
-        return;
+        return false;
     };
-    dispatch(el.asEventTarget(), event.asEvent(), frame, typ);
+    const base_event = event.asEvent();
+    base_event.acquireRef();
+    defer base_event.releaseRef(frame._page);
+
+    dispatch(el.asEventTarget(), base_event, frame, typ);
+    return base_event.getDefaultPrevented();
 }
 
 fn dispatchWheel(el: *Element, delta_x: i32, delta_y: i32, frame: *Frame) void {
diff --git a/src/mcp/tools.zig b/src/mcp/tools.zig
index 1aea5a621..4ad8c7577 100644
--- a/src/mcp/tools.zig
+++ b/src/mcp/tools.zig
@@ -1206,8 +1206,8 @@ test "MCP - Actions: click, fill, scroll, hover, press, selectOption, setChecked
         \\   'pointerup:0:0:mouse:true', 'mouseup:0:0::true', 'click:0:0:mouse:true'
         \\ ]) &&
         \\ JSON.stringify(window.seqPrevented) === JSON.stringify(['pointerdown', 'pointerup', 'click']) &&
-        \\ window.disabledMousedowned === false &&
-        \\ window.focusTargetFocused === true && window.focusAfterPlain === 'focusTarget' &&
+        \\ JSON.stringify(window.disabledEvents) === '[]' &&
+        \\ window.focusTargetFocused === true && window.plainBlurred === true &&
         \\ window.clicked === true && window.inputVal === 'hello' &&
         \\ window.changed === true && window.selChanged === 'opt2' &&
         \\ window.scrolled === true &&
diff --git a/src/script/Runtime.zig b/src/script/Runtime.zig
index eb91419fe..1836179ea 100644
--- a/src/script/Runtime.zig
+++ b/src/script/Runtime.zig
@@ -1441,7 +1441,13 @@ test "agent script runtime: tool errors throw and stop execution" {
     );
 }
 
-test "agent script runtime: selector click preserves pointer mouse semantics" {
+// Complements the fixture-driven MCP test in tools.zig: here the nodes are
+// created at runtime. Covers the ancestor walk, blur-to-body on a non-focusable
+// node, tabindex=-1 still mouse-focusable, an unparsable tabindex on a plain div
+// not focusable but on a button falling through to native focusability,
+// preventDefault() on mousedown preserving focus, editing hosts winning over
+// their contents, and an explicit tabindex on a non-HTML (SVG) element.
+test "agent script runtime: mousedown focus follows mouse-focusability rules" {
     defer testing.test_session.closeAllPages();
 
     var registry = CDPNode.Registry.init(testing.allocator);
@@ -1453,41 +1459,44 @@ test "agent script runtime: selector click preserves pointer mouse semantics" {
     try runTestScript(runtime,
         \\const page = new Page();
         \\await page.goto("http://localhost:9582/src/browser/tests/mcp_actions.html");
-        \\page.click("#btn");
-        \\const full = page.evaluate("JSON.stringify(window.seq)");
-        \\if (full !== '["pointerdown:0:1:mouse:true","mousedown:0:1::true","pointerup:0:0:mouse:true","mouseup:0:0::true","click:0:0:mouse:true"]') throw new Error("wrong full click sequence: " + full);
-        \\page.click("#btnPreventDefault");
-        \\const suppressed = page.evaluate("JSON.stringify(window.seqPrevented)");
-        \\if (suppressed !== '["pointerdown","pointerup","click"]') throw new Error("wrong suppressed sequence: " + suppressed);
-        \\page.click("#btnDisabled");
-        \\if (page.evaluate("String(window.disabledMousedowned)") !== "false") throw new Error("disabled button received mousedown");
-        \\page.click("#focusTarget");
-        \\if (page.evaluate("document.activeElement.id") !== "focusTarget") throw new Error("mousedown focus default action was lost");
-    );
-}
-
-// Different workflow from the fixture above: the tabindex node is created at
-// runtime, the click lands on a child (ancestor walk), a following click on a
-// non-focusable node must not steal focus, and tabindex=-1 is still mouse-focusable.
-test "agent script runtime: dynamic tabindex child click focuses ancestor" {
-    defer testing.test_session.closeAllPages();
-
-    var registry = CDPNode.Registry.init(testing.allocator);
-    defer registry.deinit();
-
-    const runtime = try Runtime.init(testing.allocator, testing.test_app, testing.test_session, &registry);
-    defer runtime.deinit();
-
-    try runTestScript(runtime,
-        \\const page = new Page();
-        \\await page.goto("http://localhost:9582/src/browser/tests/mcp_actions.html");
-        \\page.evaluate("const p=document.createElement('div');p.id='dynFocus';p.setAttribute('tabindex','0');const s=document.createElement('span');s.id='dynChild';s.textContent='x';p.appendChild(s);document.body.appendChild(p);const n=document.createElement('div');n.id='dynNeg';n.setAttribute('tabindex','-1');n.textContent='neg';document.body.appendChild(n)");
+        \\page.evaluate("const p=document.createElement('div');p.id='dynFocus';p.setAttribute('tabindex','0');const s=document.createElement('span');s.id='dynChild';s.textContent='x';p.appendChild(s);document.body.appendChild(p);const n=document.createElement('div');n.id='dynNeg';n.setAttribute('tabindex','-1');n.textContent='neg';document.body.appendChild(n);const b=document.createElement('div');b.id='dynBad';b.setAttribute('tabindex','abc');b.textContent='bad';document.body.appendChild(b);const btn=document.createElement('button');btn.id='dynBadBtn';btn.setAttribute('tabindex','abc');btn.textContent='badbtn';btn.addEventListener('mouseup',function(){window.badBtnFocusAtMouseup=document.activeElement.id;});document.body.appendChild(btn)");
         \\page.click("#dynChild");
         \\if (page.evaluate("document.activeElement.id") !== "dynFocus") throw new Error("child click did not focus tabindex ancestor: " + page.evaluate("document.activeElement && document.activeElement.id"));
         \\page.click("#plain");
-        \\if (page.evaluate("document.activeElement.id") !== "dynFocus") throw new Error("plain click stole focus: " + page.evaluate("document.activeElement && document.activeElement.id"));
+        \\if (page.evaluate("String(document.activeElement === document.body)") !== "true") throw new Error("plain click did not blur to body: " + page.evaluate("document.activeElement && document.activeElement.id"));
         \\page.click("#dynNeg");
         \\if (page.evaluate("document.activeElement.id") !== "dynNeg") throw new Error("tabindex=-1 was not mouse-focusable: " + page.evaluate("document.activeElement && document.activeElement.id"));
+        \\page.click("#dynBad");
+        \\if (page.evaluate("String(document.activeElement === document.body)") !== "true") throw new Error("unparsable tabindex was mouse-focusable: " + page.evaluate("document.activeElement && document.activeElement.id"));
+        \\page.click("#dynBadBtn");
+        \\// Sampled at mouseup, not after the click: a button's click activation
+        \\// behavior focuses it unconditionally, which would mask what mousedown did.
+        \\if (page.evaluate("window.badBtnFocusAtMouseup") !== "dynBadBtn") throw new Error("unparsable tabindex on a native button lost native mousedown focusability: " + page.evaluate("String(window.badBtnFocusAtMouseup)"));
+        \\// Toolbar idiom: preventDefault() on mousedown preserves existing focus
+        \\page.evaluate("const t=document.createElement('div');t.id='toolbarBtn';t.addEventListener('mousedown',function(e){e.preventDefault();});document.body.appendChild(t)");
+        \\page.click("#inp");
+        \\if (page.evaluate("document.activeElement.id") !== "inp") throw new Error("setup failed: activeElement not inp");
+        \\page.click("#toolbarBtn");
+        \\if (page.evaluate("document.activeElement.id") !== "inp") throw new Error("preventDefault on mousedown did not protect focus (toolbar idiom): " + page.evaluate("document.activeElement && document.activeElement.id"));
+        \\// Editing hosts: the click focuses the host, not what is inside it.
+        \\// Verified against Chrome 152 with trusted CDP input: a plain span, a
+        \\// button, a [tabindex] div and an <a href> inside a contenteditable all
+        \\// leave focus on the host, and a nested host resolves to the OUTER one.
+        \\page.evaluate("const h=document.createElement('div');h.id='dynHost';h.setAttribute('contenteditable','true');const hs=document.createElement('span');hs.id='dynHostSpan';hs.textContent='hs';h.appendChild(hs);document.body.appendChild(h)");
+        \\page.click("#dynHostSpan");
+        \\if (page.evaluate("document.activeElement.id") !== "dynHost") throw new Error("span inside contenteditable did not focus host: " + page.evaluate("document.activeElement && document.activeElement.id"));
+        \\// Nested contenteditable: the OUTER host wins, not the inner one.
+        \\page.evaluate("const out=document.createElement('div');out.id='dynOuter';out.setAttribute('contenteditable','true');const inn=document.createElement('div');inn.id='dynInner';inn.setAttribute('contenteditable','true');const is=document.createElement('span');is.id='dynInnerSpan';is.textContent='is';inn.appendChild(is);out.appendChild(inn);document.body.appendChild(out)");
+        \\page.click("#dynInnerSpan");
+        \\if (page.evaluate("document.activeElement.id") !== "dynOuter") throw new Error("nested contenteditable did not focus the outer host: " + page.evaluate("document.activeElement && document.activeElement.id"));
+        \\// An explicit tabindex is focusable on a non-HTML element too: the
+        \\// HTML-only guard must not shadow it, or the new blur fallback would
+        \\// drop focus to body on a click Chrome focuses.
+        \\page.evaluate("const svg=document.createElementNS('http://www.w3.org/2000/svg','svg');const r=document.createElementNS('http://www.w3.org/2000/svg','rect');r.id='dynSvgRect';r.setAttribute('tabindex','0');r.setAttribute('width','100');r.setAttribute('height','40');svg.appendChild(r);document.body.appendChild(svg)");
+        \\page.click("#inp");
+        \\if (page.evaluate("document.activeElement.id") !== "inp") throw new Error("setup failed: activeElement not inp");
+        \\page.click("#dynSvgRect");
+        \\if (page.evaluate("document.activeElement.id") !== "dynSvgRect") throw new Error("svg [tabindex] click did not focus the svg element: " + page.evaluate("document.activeElement && document.activeElement.id"));
     );
 }