diff --git a/backend/src/SDLBackend.zig b/backend/src/SDLBackend.zig
index 8bb90bc4..c9d447ce 100644
--- a/backend/src/SDLBackend.zig
+++ b/backend/src/SDLBackend.zig
@@ -18,6 +18,8 @@ const GpuRenderer = @import("GpuRenderer.zig");
 pub const viewport_map = @import("viewport_map.zig");
 /// The OS windows besides the main one an app draws with (`Viewport`).
 pub const viewports = @import("viewports.zig");
+/// `dvui.osWindow` as a window of its own from the one frame (`osWindowFloating`).
+pub const os_windows = @import("os_windows.zig");
 /// What this backend keeps count of as it runs (`health`).
 pub const Health = @import("Health.zig");
 
@@ -97,7 +99,7 @@ clock_ahead_ns: i128 = 0,
 /// Last known window rect while not maximized/fullscreen/minimized, tracked
 /// from move/resize events
 window_geometry: WindowGeometry = .{},
-// Set by `initWindow` and `initWindowSecondary` for use by eventual child window.
+// Set by `initWindow`.
 init_opts_save: ?InitOptions = null,
 /// The OS windows besides this one that show part of its frame (`Viewport`).
 viewport_slots: [max_viewports]?Viewport = @splat(null),
@@ -490,43 +492,6 @@ pub fn initWindow(init_options: InitOptions) !SDLBackend {
     return back;
 }
 
-pub fn initWindowSecondary(parent: *SDLBackend, child_win_opts: dvui.OsWindowWidget.InitOptions) !SDLBackend {
-    const parent_opts = parent.init_opts_save orelse {
-        log.err("initWindowSecondary expects parent instance with `init_opts_save` field set (typically by `initWindow`)", .{});
-        return dvui.Backend.GenericError.BackendError;
-    };
-    const new_init_opts: SDLBackend.InitOptions = .{
-        .io = parent.io,
-        .environ_map = parent_opts.environ_map,
-
-        .size = child_win_opts.size orelse parent_opts.size,
-        .min_size = child_win_opts.min_size orelse parent_opts.min_size,
-        .max_size = child_win_opts.max_size orelse parent_opts.max_size,
-        .vsync = parent_opts.vsync,
-        .title = child_win_opts.title orelse parent_opts.title,
-        .org = parent_opts.org,
-        .icon = child_win_opts.icon orelse parent_opts.icon,
-        .hidden = child_win_opts.hidden,
-        .fullscreen = child_win_opts.fullscreen,
-        .transparent = parent_opts.transparent,
-        .sdl_init = false,
-        // only the primary window persists its geometry
-        .persist_window_geometry = false,
-    };
-    // Secondary windows share the primary's GPU device: textures are per dvui window, but one
-    // device can drive any number of claimed windows.
-    const new = try createWindowRenderer(new_init_opts, parent.gpu);
-
-    var back = init(dvui.io, new.win, new.gpu);
-    back.init_opts_save = new_init_opts;
-    back.window_geometry = new.saved_geometry orelse .{};
-    back.sdl_quit = false;
-    back.log_events = parent.log_events;
-
-    try configureBackend(&back, new_init_opts);
-
-    return back;
-}
 
 fn createWindowRenderer(options: InitOptions, share_device_of: ?*GpuRenderer) !struct {
     win: *c.SDL_Window,
@@ -775,7 +740,7 @@ pub const WindowGeometry = struct {
     }
 };
 
-// Common configuration part for both `initWindow` and `initWindowSecondary`
+// The configuration `initWindow` applies.
 fn configureBackend(back: *SDLBackend, options: InitOptions) !void {
     var hidden = options.hidden;
     var show_window_in_begin = false;
@@ -1080,6 +1045,17 @@ fn addEventWinRecursive(self: *SDLBackend, event: *c.SDL_Event, win: *dvui.Windo
     return false;
 }
 
+// ---------------------------------------------------------------------------------------------
+// dvui's OS windows
+
+/// A `dvui.osWindow`, which dvui draws as a floating window here: this backend makes no
+/// `dvui.Window` of its own for one (no `initWindowSecondary`), so it is a floating window in the
+/// one frame, and `os_windows` shows it in an OS window of its own. dvui calls this each frame it is
+/// drawn, with the header it is moved by (physical).
+pub fn osWindowFloating(_: *SDLBackend, id: dvui.Id, header: dvui.Rect.Physical, opts: dvui.OsWindowWidget.InitOptions) void {
+    os_windows.named(id, header, opts.title);
+}
+
 // ---------------------------------------------------------------------------------------------
 // Viewports (fizzy's own; see `Viewport`)
 
@@ -3596,10 +3572,12 @@ fn appIterate(_: ?*anyopaque) callconv(.c) c.SDL_AppResult {
     };
 
     const app = dvui.App.get() orelse unreachable;
+    os_windows.beforeFrame();
     var res = app.frameFn() catch |err| {
         log.err("dvui.App.frameFn failed: {any}", .{err});
         return c.SDL_APP_FAILURE;
     };
+    os_windows.afterFrame();
 
     live_resize_trace.overlay();
 
diff --git a/backend/src/os_windows.zig b/backend/src/os_windows.zig
new file mode 100644
index 00000000..b491d301
--- /dev/null
+++ b/backend/src/os_windows.zig
@@ -0,0 +1,185 @@
+//! `dvui.osWindow` on this backend: each is a floating window in the one frame (dvui's fallback,
+//! as this backend makes no `dvui.Window` of its own for one), shown in an OS window of its own
+//! (`viewports`) that looks just as it does inside the main window — dvui's header and close
+//! button, no OS title bar (`Frame.app`). The app writes plain dvui; on a backend without OS
+//! windows the same floating window stays in the main window.
+//!
+//! dvui says which floating windows are OS windows as they draw (`named`, from
+//! `SDLBackend.osWindowFloating`). Around the app's frame (`SDLBackend.appIterate`, or an app's
+//! own loop):
+//!
+//! - `beforeFrame`: a window the OS moved takes its floating window with it (`osPlaced`), and each
+//!   window's band is a screen of dvui's (`dvui.screensSet`), so dvui keeps the floating window in
+//!   it; one being resized holds the pointer in its band (`pinPointer`);
+//! - `afterFrame`: dvui's dialogs and toasts made (`Window.drawRetained`); a window whose floating
+//!   window was not drawn — closed — goes; each one named and not yet in a window gets one over
+//!   where it is (`viewports.open`), drawn in that window's band from the next frame; and each
+//!   window is put where its floating window is (`viewports.place`), told its header is where the
+//!   OS moves it from (`hints`), and handed its picture: every subwindow in its band, taken out of
+//!   the frame (`viewports.Picture`).
+//!
+//! dvui keeps where each floating window is (`_rect` in its data, by its id): moved into the
+//! window's band, and read back after the frame.
+const dvui = @import("dvui");
+const viewports = @import("viewports.zig");
+
+/// As many as there are viewports. Past that, a floating window stays in the main window.
+const max_outs = 8;
+
+/// A floating window in an OS window of its own, by its dvui id.
+const Out = struct {
+    id: dvui.Id,
+    viewport: *viewports.Viewport,
+    target: ?dvui.Texture.Target = null,
+    /// Opened this frame: drawn in the main window still, in its band from the next.
+    fresh: bool = true,
+};
+var outs: [max_outs]?Out = @splat(null);
+
+/// The floating windows dvui named as OS windows this frame (`named`), with their headers
+/// (physical) and titles.
+const Named = struct { id: dvui.Id, header: dvui.Rect.Physical, title: [64:0]u8 };
+var named_list: [max_outs]Named = undefined;
+var named_n: usize = 0;
+
+/// The pointer is pinned to a window's band by `beforeFrame`, to be let go once nothing holds it.
+var pinned = false;
+
+/// dvui drew floating window `id` for an OS window this frame (`dvui.osWindow`), moved by `header`.
+pub fn named(id: dvui.Id, header: dvui.Rect.Physical, title: ?[:0]const u8) void {
+    if (named_n == named_list.len) return;
+    var n: Named = .{ .id = id, .header = header, .title = @splat(0) };
+    const t = title orelse "";
+    const len = @min(t.len, n.title.len);
+    @memcpy(n.title[0..len], t[0..len]);
+    named_list[named_n] = n;
+    named_n += 1;
+}
+
+fn natural(r: viewports.Rect, s: f32) dvui.Rect {
+    return .{ .x = r.x / s, .y = r.y / s, .w = r.w / s, .h = r.h / s };
+}
+
+fn physical(r: dvui.Rect, s: f32) viewports.Rect {
+    return .{ .x = r.x * s, .y = r.y * s, .w = r.w * s, .h = r.h * s };
+}
+
+/// After `dvui.Window.begin`, before the app's frame.
+pub fn beforeFrame() void {
+    named_n = 0;
+    const s = dvui.windowNaturalScale();
+    var screens: [max_outs]dvui.Rect.Natural = undefined;
+    var n: usize = 0;
+    var pin: ?*viewports.Viewport = null;
+    for (&outs) |*slot| {
+        const o = if (slot.*) |*o| o else continue;
+        if (viewports.osPlaced(o.viewport)) |fr| dvui.dataSet(null, o.id, "_rect", natural(fr, s));
+        _ = viewports.osMoveEnded(o.viewport);
+        const r = dvui.dataGet(null, o.id, "_rect", dvui.Rect) orelse continue;
+        screens[n] = .{ .x = r.x, .y = r.y, .w = r.w, .h = r.h };
+        n += 1;
+        // Resized from its edges, it holds the pointer: read in its band till it lets go, even
+        // past its window's edge.
+        if (dvui.captured(o.id)) pin = o.viewport;
+    }
+    // Only with windows of its own: an app keeping screens of its own (fizzy's floats) sets them.
+    if (n > 0) dvui.screensSet(screens[0..n]);
+    if (pin) |vp| {
+        viewports.pinPointer(.{ .viewport = vp });
+        pinned = true;
+    } else if (pinned) {
+        viewports.pinPointer(.none);
+        pinned = false;
+    }
+}
+
+/// After the app's frame, before `dvui.Window.end`.
+pub fn afterFrame() void {
+    if (named_n == 0 and for (outs) |slot| {
+        if (slot != null) break false;
+    } else true) return;
+    const cw = dvui.currentWindow();
+    // Dialogs and toasts are subwindows from here, so each lands in the window it is over.
+    cw.drawRetained(.{});
+    const s = dvui.windowNaturalScale();
+
+    for (&outs) |*slot| {
+        const o = if (slot.*) |*o| o else continue;
+        const drawn = for (cw.subwindows.stack.items) |sw| {
+            if (sw.id == o.id) break sw.used;
+        } else false;
+        if (drawn) {
+            // Its close button cleared what showed it: it goes next frame, which comes now
+            // rather than at the next event.
+            if (namedOf(o.id) == null) dvui.refresh(null, @src(), null);
+            continue;
+        }
+        viewports.close(o.viewport);
+        if (o.target) |t| t.destroyLater();
+        slot.* = null;
+    }
+
+    for (named_list[0..named_n]) |*w| {
+        if (outOf(w.id) != null) continue;
+        if (!viewports.available()) break;
+        const slot = for (&outs) |*slot| {
+            if (slot.* == null) break slot;
+        } else break;
+        const r = dvui.dataGet(null, w.id, "_rect", dvui.Rect) orelse continue;
+        // Not before dvui has sized and placed it: a floating window spends its first frame
+        // measuring itself, hidden, and centers itself once (`_auto_pos`) — over the main window,
+        // which would take it out of its window's band again.
+        if (r.w < 1 or r.h < 1) continue;
+        if (dvui.dataGet(null, w.id, "_auto_pos", bool) orelse true) continue;
+        const vp = viewports.open(physical(r, s), &w.title, .app) orelse break;
+        slot.* = .{ .id = w.id, .viewport = vp };
+        dvui.dataSet(null, w.id, "_rect", natural(viewports.frameOf(vp), s));
+        dvui.refresh(null, @src(), null);
+    }
+
+    for (&outs) |*slot| {
+        const o = if (slot.*) |*o| o else continue;
+        if (o.fresh) {
+            o.fresh = false;
+            continue;
+        }
+        const r = dvui.dataGet(null, o.id, "_rect", dvui.Rect) orelse continue;
+        const shown = viewports.place(o.viewport, physical(r, s));
+        // The OS moves its window by its header, but for the close button — square at the
+        // header's height, at its right end where buttons go OK then Cancel, else its left
+        // (`dvui.windowHeader`) — and not from the floating window's own resize zones round its
+        // edge (`app_side`).
+        if (namedOf(o.id)) |w| {
+            const hd = w.header;
+            const keep_x = if (cw.button_order == .ok_cancel) hd.x + hd.w - hd.h else hd.x;
+            viewports.hints(o.viewport, .{
+                .drag = .{ .x = hd.x, .y = hd.y, .w = hd.w, .h = hd.h },
+                .keep = .{ .x = keep_x, .y = hd.y, .w = hd.h, .h = hd.h },
+                .glass = shown,
+                .edge = 0,
+                .app_side = 6 * s,
+                .app_corner = 15 * s,
+            });
+        }
+        const w: u32 = @intFromFloat(@max(1, @round(shown.w)));
+        const h: u32 = @intFromFloat(@max(1, @round(shown.h)));
+        const target = viewports.sizedTarget(&o.target, w, h) orelse continue;
+        const area: dvui.Rect.Physical = .{ .x = shown.x, .y = shown.y, .w = shown.w, .h = shown.h };
+        const picture: viewports.Picture = .begin(target, shown);
+        for (cw.subwindows.stack.items) |*sw| {
+            if (area.contains(sw.rect_pixels.center())) picture.subwindow(sw, true);
+        }
+        picture.end();
+        viewports.present(o.viewport, target);
+    }
+}
+
+fn outOf(id: dvui.Id) ?*Out {
+    for (&outs) |*slot| if (slot.*) |*o| if (o.id == id) return o;
+    return null;
+}
+
+fn namedOf(id: dvui.Id) ?*const Named {
+    for (named_list[0..named_n]) |*w| if (w.id == id) return w;
+    return null;
+}
diff --git a/docs/DEPENDENCIES.md b/docs/DEPENDENCIES.md
index 7c026a80..3a41e8d2 100644
--- a/docs/DEPENDENCIES.md
+++ b/docs/DEPENDENCIES.md
@@ -69,18 +69,31 @@ backend and never link SDL, so an SDL bump is never an SDK release and never mov
 6. **screensSet: floating widgets can be kept on screens besides the window** (`a90bc70`).
    `dvui.screensSet(rects)` lists areas besides the window that are screens of their own;
    floating windows, menus and tooltips place, clip and dim against `dvui.screenFor` (the one
-   holding their middle, else `windowRect`). Not yet used by fizzy, whose `core.screens` and
-   widget forks do the same. Upstream: branch `screens-set`, to propose. Test: "a floating window
-   on another screen (dvui.screensSet) stays on it".
+   holding their middle, else `windowRect`). Popout sets each float window's band as one (#325),
+   and the backend's `os_windows` each `dvui.osWindow`'s. Upstream: branch `screens-set`, to
+   propose. Test: "a floating window on another screen (dvui.screensSet) stays on it".
+7. **OsWindowWidget: a child window is deinit before its backend** (`f0f498a`). `ChildOsWindow.deinit`
+   freed the backend first, then the `dvui.Window`, whose deinit gives its textures (the font
+   atlases) back to that backend: closing any `dvui.osWindow` on a backend with secondary windows
+   crashed. Upstream: worth proposing on its own.
+8. **osWindow: the fallback floating window is the window asked for, and its backend hears of it**
+   (`f646ec0`). Where a backend makes no OS window of its own, `dvui.osWindow` falls back to a
+   floating window, which now takes the window's size, least and most size, `id_extra`, a close
+   button on its `open_flag` (the next frame asked for at once), and steps past one already there;
+   and the backend hears of it each frame (`Backend.osWindowFloating`: its id, the header it is
+   moved by, the options). Fizzy's backend makes no secondary `dvui.Window`, so every
+   `dvui.osWindow` takes this path, and `backend/src/os_windows.zig` shows the floating window in
+   an OS window of its own. Upstream: to propose with `run-dvui` (fizzyedit/example-app) as the
+   demonstration.
 
 Each of 5 and 6 is also a branch of its own on upstream `main` (`window-draw-retained`,
 `screens-set`), from which the upstream PR is opened.
 
 Tags: `fizzy-sdk-0.2.13` → `712f7f7` (the stack before this rebase, still what SDK ≤ 0.2.15
 builds); `fizzy-sdk-0.2.16` → `4428108` (SDK 0.2.16 to 0.2.18); `fizzy-sdk-0.2.19` →
-`f8b32db`; `fizzy-sdk-0.2.19-2` → `a90bc70`, what `sdk/build.zig.zon` pins now (0.2.19 was not
-released yet, and a tag never moves, so the second pin of one version takes a suffix, as the SDL
-fork's tags do).
+`f8b32db`; `fizzy-sdk-0.2.19-2` → `a90bc70` (0.2.19 was not released yet, and a tag never
+moves, so the second pin of one version takes a suffix, as the SDL fork's tags do; SDK 0.2.19 to
+0.2.22); `fizzy-sdk-0.2.23` → `f646ec0`, what `sdk/build.zig.zon` pins now.
 
 Fizzy builds dvui in its `custom` backend mode on every target and links its own backends
 (`backend/`, `src/backend/WebBackend.zig` + `web/web.js`), so dvui's `sdl3` and `web`
diff --git a/sdk/build.zig.zon b/sdk/build.zig.zon
index 44f42f1c..b48e2e3b 100644
--- a/sdk/build.zig.zon
+++ b/sdk/build.zig.zon
@@ -39,9 +39,9 @@
         // `fizzy-sdk-<version>` tag in the fork before the pin lands. `fizzy-dev` itself stays a
         // working branch and can be rebased freely — the tag, never.
         .dvui = .{
-            // fizzy-sdk-0.2.19-2
-            .url = "https://github.com/foxnne/dvui-dev/archive/a90bc701c5b9.tar.gz",
-            .hash = "dvui-0.5.0-dev-AQFJmfUrBAEB1joV1vjYrG_e_jx27JfNi9Bdr9ldPPGn",
+            // fizzy-sdk-0.2.23
+            .url = "https://github.com/foxnne/dvui-dev/archive/f646ec0b17899a2c2f222ecce834c82e235e0486.tar.gz",
+            .hash = "dvui-0.5.0-dev-AQFJmTQyBAHtzJRJ2BzYtusSfj5mYzF4owYGcDHfyNY_",
             //.path = "../../dvui-dev",
         },
         .zf = .{