diff --git a/examples/gallery/app.go b/examples/gallery/app.go
index 29e8bda..dba04b1 100644
--- a/examples/gallery/app.go
+++ b/examples/gallery/app.go
@@ -33,13 +33,18 @@ type gallery struct {
 	events   []event
 	scrolls  map[string]*ui.ScrollState
 	overture overtureState
+	// Composition state lives here so it survives page switches.
+	cSettings settingsDemo
+	cFiles    filesDemo
+	cForm     formSubmitDemo
 }
 
 // densities maps the density control's segments to theme densities.
 var densities = []theme.Density{theme.Compact, theme.Default, theme.Comfortable}
 
 func newGallery() *gallery {
-	g := &gallery{pages: catalog(), byID: map[string]int{}, selected: overtureID, density: 1, scrolls: map[string]*ui.ScrollState{}}
+	g := &gallery{pages: catalog(), byID: map[string]int{}, selected: overtureID, density: 1, scrolls: map[string]*ui.ScrollState{},
+		cSettings: newSettingsDemo(), cFiles: newFilesDemo(), cForm: newFormSubmitDemo()}
 	for i, p := range g.pages {
 		if _, dup := g.byID[p.ID]; dup {
 			panic("gallery: duplicate page " + p.ID)
@@ -138,6 +143,12 @@ func (g *gallery) content(c *ui.Context) {
 		switch g.selected {
 		case overtureID:
 			g.overturePage(c)
+		case settingsID:
+			g.compositePage(c, settingsID, g.settingsView)
+		case filesID:
+			g.compositePage(c, filesID, g.filesView)
+		case formID:
+			g.compositePage(c, formID, g.formView)
 		default:
 			i, ok := g.byID[g.selected]
 			if !ok {
diff --git a/examples/gallery/composite_files.go b/examples/gallery/composite_files.go
new file mode 100644
index 0000000..b42b472
--- /dev/null
+++ b/examples/gallery/composite_files.go
@@ -0,0 +1,358 @@
+package main
+
+import (
+	"cmp"
+	"fmt"
+	"os"
+	"path/filepath"
+	"slices"
+	"strings"
+	"time"
+
+	"github.com/egoist/mygo/ui"
+
+	mujica "mujicaui"
+	"mujicaui/icons"
+	"mujicaui/theme"
+)
+
+const filesID = "c-files"
+
+type fileEntry struct {
+	ID       int
+	Name     string
+	Size     int64
+	Modified time.Time
+}
+
+type filesDemo struct {
+	entries  []fileEntry
+	next     int
+	version  int
+	query    string
+	table    mujica.DataTableState[int]
+	dropped  []mujica.DroppedFile
+	picked   []string
+	renaming bool
+	renameID int
+	newName  string
+	deleting bool
+	doomed   []int
+}
+
+func filesSample() []fileEntry {
+	at := func(m time.Month, d, h int) time.Time { return time.Date(2026, m, d, h, 0, 0, 0, time.UTC) }
+	return []fileEntry{
+		{1, "setlist-masquerade.pdf", 182_400, at(9, 28, 21)},
+		{2, "rehearsal-0412.wav", 48_211_968, at(4, 12, 19)},
+		{3, "stage-plot.png", 2_406_400, at(8, 3, 14)},
+		{4, "lyrics-draft.md", 6_912, at(10, 1, 23)},
+		{5, "venue-contract.docx", 96_256, at(7, 19, 10)},
+		{6, "overture-score.musicxml", 731_136, at(9, 30, 2)},
+		{7, "press-kit.zip", 18_874_368, at(6, 6, 16)},
+		{8, "budget-2026.xlsx", 41_984, at(5, 22, 9)},
+	}
+}
+
+func newFilesDemo() filesDemo { return filesDemo{entries: filesSample(), next: 9} }
+
+// fileSize writes a byte count the way a file manager does.
+func fileSize(n int64) string {
+	switch {
+	case n < 1<<10:
+		return fmt.Sprintf("%d B", n)
+	case n < 1<<20:
+		return fmt.Sprintf("%.1f KB", float64(n)/(1<<10))
+	default:
+		return fmt.Sprintf("%.1f MB", float64(n)/(1<<20))
+	}
+}
+
+func (g *gallery) fileColumns(c *ui.Context) []mujica.DataColumn[fileEntry] {
+	return []mujica.DataColumn[fileEntry]{
+		{ID: "name", Title: g.t("Name", "名称"), MinWidth: 200, Sortable: true,
+			Text:    func(f fileEntry) string { return f.Name },
+			Compare: func(a, b fileEntry) int { return cmp.Compare(a.Name, b.Name) },
+			Cell: func(f fileEntry) {
+				ui.Row(c).Gap(8).AlignItems(ui.Center).MinWidth(0).Children(func() {
+					ui.Icon(c, icons.Must("file")).Size(16, 16).TextColor(mujica.Tokens(c).TextMuted)
+					ui.Text(c, f.Name).SingleLine()
+				})
+			}},
+		{ID: "size", Title: g.t("Size", "大小"), Width: 110, Align: ui.End, Sortable: true,
+			Text:    func(f fileEntry) string { return fileSize(f.Size) },
+			Compare: func(a, b fileEntry) int { return cmp.Compare(a.Size, b.Size) }},
+		{ID: "modified", Title: g.t("Modified", "修改时间"), Width: 170, Sortable: true,
+			Text:    func(f fileEntry) string { return f.Modified.Format("2006-01-02 15:04") },
+			Compare: func(a, b fileEntry) int { return a.Modified.Compare(b.Modified) }},
+	}
+}
+
+// targets are the checked rows, or else the focused row.
+func (s *filesDemo) targets() []int {
+	if s.table.Selection.Len() > 0 {
+		return slices.Sorted(s.table.Selection.All())
+	}
+	if id, ok := s.table.Selected(); ok {
+		return []int{id}
+	}
+	return nil
+}
+
+func (s *filesDemo) entry(id int) *fileEntry {
+	i := slices.IndexFunc(s.entries, func(f fileEntry) bool { return f.ID == id })
+	if i < 0 {
+		panic(fmt.Sprintf("gallery: no file %d", id))
+	}
+	return &s.entries[i]
+}
+
+// add appends a file unless one with its name is listed; it reports whether it did.
+func (s *filesDemo) add(path string, size int64, at time.Time) bool {
+	name := filepath.Base(path)
+	if slices.ContainsFunc(s.entries, func(f fileEntry) bool { return f.Name == name }) {
+		return false
+	}
+	s.entries = append(s.entries, fileEntry{s.next, name, size, at})
+	s.next++
+	s.version++
+	return true
+}
+
+func (g *gallery) filesView(c *ui.Context, log func(string)) {
+	s := &g.cFiles
+	k := mujica.Tokens(c)
+	cols := g.fileColumns(c)
+	targets := s.targets()
+	ui.Row(c).FillWidth().Gap(12).AlignItems(ui.Center).Children(func() {
+		mujica.Toolbar(c, mujica.ToolbarOptions{Label: g.t("File actions", "文件操作")}, func() {
+			g.fileActions(c, log, targets, func(m *mujica.PopupMenu) { g.fileMenu(m, log, targets) })
+		}).Grow(1)
+		before := s.query
+		mujica.SearchInput(c, &s.query, mujica.SearchInputOptions{Placeholder: g.t("Filter files", "筛选文件")}).Element.Width(240)
+		if s.query != before {
+			log(fmt.Sprintf("filter %q", s.query))
+		}
+	})
+	s.table.Filter = s.query
+	shown := len(mujica.DataTableRows(s.entries, cols, s.table.Sort, s.query))
+	switch {
+	case len(s.entries) == 0:
+		if mujica.EmptyState(c, mujica.EmptyStateOptions{Kind: mujica.EmptyNoData, Title: g.t("No files", "没有文件"),
+			Description: g.t("Drop files below or choose some to add them.", "将文件拖到下方，或选取文件以添加。"),
+			Action:      g.t("Restore samples", "恢复示例")}).Action {
+			g.restoreFiles(log)
+		}
+	case shown == 0:
+		if mujica.EmptyState(c, mujica.EmptyStateOptions{Kind: mujica.EmptyNoResults, Query: s.query, Action: g.t("Clear filter", "清除筛选")}).Action {
+			s.query = ""
+			log("filter cleared")
+		}
+	default:
+		v := mujica.DataTable(c, &s.table, s.entries, mujica.DataTableOptions[fileEntry, int]{
+			Columns: cols, Key: func(f fileEntry) int { return f.ID }, Multiple: true, Version: s.version,
+		})
+		v.FillWidth().Height(430)
+		mujica.ContextMenu(c, v.Element, mujica.ContextMenuOptions{}, func(m *mujica.PopupMenu) { g.fileMenu(m, log, targets) })
+		if v.Changed() {
+			log(fmt.Sprintf("selection %d checked", s.table.Selection.Len()))
+		}
+		if v.SortChanged() {
+			log(fmt.Sprintf("sort %s descending=%v", s.table.Sort.Column, s.table.Sort.Descending))
+		}
+		if v.Submitted() && len(targets) == 1 {
+			g.startRename(log, targets[0])
+		}
+	}
+	var size int64
+	for _, f := range s.entries {
+		size += f.Size
+	}
+	mujica.StatusBar(c, mujica.StatusBarOptions{
+		Left: []mujica.StatusItem{
+			{ID: "count", Icon: icons.Must("folder"), Text: fmt.Sprintf(g.t("%d files · %s", "%d 个文件 · %s"), len(s.entries), fileSize(size))},
+			{ID: "shown", Text: fmt.Sprintf(g.t("%d shown", "显示 %d 个"), shown), Secondary: true},
+		},
+		Right: []mujica.StatusItem{{ID: "selected", Text: fmt.Sprintf(g.t("%d selected", "已选 %d 个"), s.table.Selection.Len())}},
+	}).Radius(theme.CardRadius).Border(theme.BorderWidth, k.Border)
+	g.fileAdders(c, log)
+	g.renameDialog(c, log)
+	g.deleteDialog(c, log)
+}
+
+// fileActions fills the toolbar; menu fills the More dropdown, shared with the context menu.
+func (g *gallery) fileActions(c *ui.Context, log func(string), targets []int, menu func(m *mujica.PopupMenu)) {
+	mujica.ToolbarGroup(c, func() {
+		if mujica.ToolbarButton(c, g.t("Rename", "重命名"), mujica.ToolbarButtonOptions{Icon: icons.Must("file-text"), ShowLabel: true, Disabled: len(targets) != 1}).Clicked() {
+			g.startRename(log, targets[0])
+		}
+		if mujica.ToolbarButton(c, g.t("Delete", "删除"), mujica.ToolbarButtonOptions{Icon: icons.Must("trash-2"), ShowLabel: true, Disabled: len(targets) == 0}).Clicked() {
+			g.startDelete(log, targets)
+		}
+	})
+	mujica.ToolbarSeparator(c)
+	mujica.DropdownMenu(c, g.t("Actions", "操作"), mujica.DropdownMenuOptions{Icon: icons.Must("ellipsis")}, menu)
+}
+
+// fileMenu holds every file action; the dropdown and the context menu share it.
+func (g *gallery) fileMenu(m *mujica.PopupMenu, log func(string), targets []int) {
+	s := &g.cFiles
+	if m.Item(g.t("Rename…", "重命名…"), mujica.PopupMenuItemOptions{Disabled: len(targets) != 1}) {
+		g.startRename(log, targets[0])
+	}
+	if m.Item(g.t("Delete…", "删除…"), mujica.PopupMenuItemOptions{Disabled: len(targets) == 0}) {
+		g.startDelete(log, targets)
+	}
+	if m.Item(g.t("Select all", "全选"), mujica.PopupMenuItemOptions{Disabled: len(s.entries) == 0}) {
+		for _, f := range s.entries {
+			s.table.Selection.Add(f.ID)
+		}
+		log(fmt.Sprintf("selected all %d", len(s.entries)))
+	}
+	if m.Item(g.t("Clear selection", "清除选择"), mujica.PopupMenuItemOptions{Disabled: s.table.Selection.Len() == 0}) {
+		s.table.Selection.Clear()
+		log("selection cleared")
+	}
+	if m.Item(g.t("Restore samples", "恢复示例"), mujica.PopupMenuItemOptions{}) {
+		g.restoreFiles(log)
+	}
+}
+
+func (g *gallery) restoreFiles(log func(string)) {
+	s := &g.cFiles
+	s.entries, s.next, s.query = filesSample(), 9, ""
+	s.table.Selection.Clear()
+	s.version++
+	log("samples restored")
+}
+
+// fileAdders are the drop zone and the picker; both only list files, nothing is uploaded.
+func (g *gallery) fileAdders(c *ui.Context, log func(string)) {
+	s := &g.cFiles
+	mujica.Card(c, mujica.CardOptions{Title: g.t("Add files", "添加文件")}, func() {
+		ui.Text(c, g.t("Files are checked and listed, never read or uploaded.", "文件只做校验并列出，不会读取或上传。")).TextColor(mujica.Tokens(c).TextMuted)
+		if mujica.FileDropZone(c, &s.dropped, mujica.FileDropZoneOptions{MaxFiles: 8, MaxSize: 50 << 20,
+			Hint: g.t("Drop files here to list them", "将文件拖到此处以列出")}).Changed() {
+			for _, f := range s.dropped {
+				g.addFile(c, log, f.Path, f.Size, time.Now())
+			}
+			s.dropped = nil
+		}
+		p := mujica.FilePicker(c, &s.picked, mujica.FilePickerOptions{Multiple: true, Label: g.t("Choose files…", "选取文件…")})
+		if p.Canceled() {
+			log("picker canceled")
+		}
+		if p.Changed() {
+			for _, path := range s.picked {
+				info, err := os.Stat(path)
+				if err != nil {
+					mujica.ShowToast(c, mujica.ToastMessage{Severity: mujica.SeverityError, Message: err.Error()})
+					log("stat failed: " + err.Error())
+					continue
+				}
+				g.addFile(c, log, path, info.Size(), info.ModTime())
+			}
+			s.picked = nil
+		}
+	})
+}
+
+func (g *gallery) addFile(c *ui.Context, log func(string), path string, size int64, at time.Time) {
+	if g.cFiles.add(path, size, at) {
+		log("added " + filepath.Base(path))
+		return
+	}
+	log("skipped duplicate " + filepath.Base(path))
+	mujica.ShowToast(c, mujica.ToastMessage{ID: "dup-" + path, Severity: mujica.SeverityWarning,
+		Message: fmt.Sprintf(g.t("%s is already listed", "%s 已在列表中"), filepath.Base(path))})
+}
+
+func (g *gallery) startRename(log func(string), id int) {
+	s := &g.cFiles
+	s.renaming, s.renameID, s.newName = true, id, s.entry(id).Name
+	log("rename " + s.newName)
+}
+
+// renameError checks a new name against the others in the list.
+func (g *gallery) renameError() string {
+	s := &g.cFiles
+	name := strings.TrimSpace(s.newName)
+	switch {
+	case name == "":
+		return g.t("Enter a name.", "请输入名称。")
+	case strings.ContainsAny(name, `/\`):
+		return g.t("A name cannot contain / or \\.", "名称不能包含 / 或 \\。")
+	case slices.ContainsFunc(s.entries, func(f fileEntry) bool { return f.Name == name && f.ID != s.renameID }):
+		return g.t("Another file has this name.", "已有同名文件。")
+	}
+	return ""
+}
+
+func (g *gallery) renameDialog(c *ui.Context, log func(string)) {
+	s := &g.cFiles
+	if !s.renaming {
+		return
+	}
+	bad := g.renameError()
+	commit := func() {
+		if bad != "" {
+			return
+		}
+		f := s.entry(s.renameID)
+		log(fmt.Sprintf("renamed %s to %s", f.Name, strings.TrimSpace(s.newName)))
+		f.Name = strings.TrimSpace(s.newName)
+		s.version++
+		s.renaming = false
+	}
+	mujica.Dialog(c, &s.renaming, mujica.DialogOptions{Title: g.t("Rename file", "重命名文件"), Actions: func() {
+		if mujica.Button(c, g.t("Cancel", "取消"), mujica.ButtonOptions{Variant: mujica.Secondary}).Clicked() {
+			s.renaming = false
+			log("rename canceled")
+		}
+		if mujica.Button(c, g.t("Rename", "重命名"), mujica.ButtonOptions{Disabled: bad != ""}).Clicked() {
+			commit()
+		}
+	}}, func() {
+		mujica.FormField(c, g.t("New name", "新名称"), mujica.FormFieldOptions{Error: bad}, func() *ui.Element {
+			r := mujica.TextInput(c, &s.newName, mujica.TextInputOptions{Error: bad})
+			if r.Submitted() {
+				commit()
+			}
+			return r.Input.AutoFocus()
+		})
+	})
+}
+
+func (g *gallery) startDelete(log func(string), ids []int) {
+	s := &g.cFiles
+	s.deleting, s.doomed = true, ids
+	log(fmt.Sprintf("delete asked for %d", len(ids)))
+}
+
+func (g *gallery) deleteDialog(c *ui.Context, log func(string)) {
+	s := &g.cFiles
+	if !s.deleting {
+		return
+	}
+	desc := fmt.Sprintf(g.t("%d files will be removed from the list.", "将从列表中移除 %d 个文件。"), len(s.doomed))
+	if len(s.doomed) == 1 {
+		desc = fmt.Sprintf(g.t("“%s” will be removed from the list.", "将从列表中移除“%s”。"), s.entry(s.doomed[0]).Name)
+	}
+	r := mujica.AlertDialog(c, &s.deleting, mujica.AlertDialogOptions{Title: g.t("Delete files?", "删除文件？"), Description: desc,
+		ConfirmLabel: g.t("Delete permanently", "永久删除")})
+	switch {
+	case r.Confirmed:
+		s.entries = slices.DeleteFunc(slices.Clone(s.entries), func(f fileEntry) bool { return slices.Contains(s.doomed, f.ID) })
+		for _, id := range s.doomed {
+			s.table.Selection.Remove(id)
+		}
+		s.version++
+		log(fmt.Sprintf("deleted %d", len(s.doomed)))
+		mujica.ShowToast(c, mujica.ToastMessage{ID: "files-deleted", Severity: mujica.SeveritySuccess,
+			Message: fmt.Sprintf(g.t("Deleted %d files", "已删除 %d 个文件"), len(s.doomed))})
+		s.doomed = nil
+	case r.Cancelled:
+		s.doomed = nil
+		log("delete canceled")
+	}
+}
diff --git a/examples/gallery/composite_form.go b/examples/gallery/composite_form.go
new file mode 100644
index 0000000..2894c3b
--- /dev/null
+++ b/examples/gallery/composite_form.go
@@ -0,0 +1,204 @@
+package main
+
+import (
+	"fmt"
+	"strings"
+	"time"
+
+	"github.com/egoist/mygo/ui"
+
+	mujica "mujicaui"
+)
+
+const formID = "c-form"
+
+// Simulated latencies of the name check and the server.
+const (
+	formCheckDelay  = 400 * time.Millisecond
+	formSubmitDelay = 900 * time.Millisecond
+)
+
+// formPhase is what the form composite shows.
+type formPhase int
+
+const (
+	formEditing formPhase = iota
+	formSucceeded
+	formFailed
+)
+
+type formSubmitDemo struct {
+	st       mujica.FormState
+	name     string
+	password string
+	debut    mujica.Date
+	tags     []string
+	terms    bool
+	failNext bool
+	phase    formPhase
+	failure  string
+	checks   chan formAsync
+	done     chan string
+}
+
+func newFormSubmitDemo() formSubmitDemo {
+	return formSubmitDemo{checks: make(chan formAsync, 8), done: make(chan string, 1)}
+}
+
+// formTaken are the names the simulated archive already holds.
+var formTaken = []string{"admin", "oblivionis"}
+
+func (g *gallery) formView(c *ui.Context, log func(string)) {
+	s := &g.cForm
+	for drained := false; !drained; {
+		select {
+		case r := <-s.checks:
+			log(fmt.Sprintf("name check v%d: %q, kept %v", r.version, r.err, s.st.Resolve("name", r.version, r.err)))
+		case e := <-s.done:
+			s.st.EndSubmit("")
+			s.phase, s.failure = formSucceeded, e
+			if e != "" {
+				s.phase = formFailed
+			}
+			log(fmt.Sprintf("server answered, error %q", e))
+		default:
+			drained = true
+		}
+	}
+	mujica.Card(c, mujica.CardOptions{Title: g.t("Audition entry", "试演报名")}, func() {
+		switch s.phase {
+		case formSucceeded:
+			g.formSuccess(c, log)
+		case formFailed:
+			g.formFailure(c, log)
+		default:
+			ui.Column(c).FillWidth().MaxWidth(640).Gap(16).Children(func() { g.formEdit(c, log) })
+		}
+	})
+}
+
+func (g *gallery) formEdit(c *ui.Context, log func(string)) {
+	s := &g.cForm
+	if mujica.Switch(c, &s.failNext, g.t("The server rejects the next submit", "服务器拒绝下一次提交"), mujica.SwitchOptions{Disabled: s.st.Submitting()}).Changed() {
+		log(fmt.Sprintf("fail next submit %v", s.failNext))
+	}
+	r := mujica.LoadingOverlay(c, s.st.Submitting(), mujica.LoadingOverlayOptions{Label: g.t("Submitting…", "正在提交…")}, func() {
+		res := mujica.Form(c, &s.st, mujica.FormOptions{Horizontal: true, SubmitLabel: g.t("Submit entry", "提交报名")}, func(f *mujica.FormScope) {
+			g.formFields(c, f, log)
+		})
+		res.Element.FillWidth()
+		if res.Reset() {
+			log("reset to initial values")
+		}
+		if res.Submitted() {
+			fail := ""
+			if s.failNext {
+				s.failNext = false
+				fail = g.t("The archive is closed for the night. Your entry was not sent.", "档案馆今夜已闭馆，报名未送达。")
+			}
+			// The password is never logged, not even its length.
+			log(fmt.Sprintf("submitted %q, debut %s, roles %q", s.name, s.debut.Format("2006-01-02"), s.tags))
+			go func() {
+				time.Sleep(formSubmitDelay)
+				s.done <- fail
+				c.Invalidate()
+			}()
+		}
+	})
+	r.Element.FillWidth()
+}
+
+func (g *gallery) formFields(c *ui.Context, f *mujica.FormScope, log func(string)) {
+	s := &g.cForm
+	mujica.FormItem(f, "name", &s.name, mujica.FormItemOptions[string]{Label: g.t("Stage name", "艺名"), Required: true,
+		Description: g.t("Checked against the archive; “Oblivionis” is taken.", "将与档案核对；“Oblivionis”已被占用。"),
+		Validate: func(v string) string {
+			if len([]rune(strings.TrimSpace(v))) < 2 {
+				return g.t("Use at least 2 characters.", "至少 2 个字符。")
+			}
+			return ""
+		},
+		Async: func(v string, version uint64) {
+			log(fmt.Sprintf("name check started v%d", version))
+			go func() {
+				time.Sleep(formCheckDelay)
+				msg := ""
+				for _, t := range formTaken {
+					if strings.EqualFold(strings.TrimSpace(v), t) {
+						msg = g.t("That name is taken.", "该名称已被占用。")
+					}
+				}
+				s.checks <- formAsync{version, msg}
+				c.Invalidate()
+			}()
+		}}, func() *ui.Element {
+		return mujica.TextInput(c, &s.name, mujica.TextInputOptions{}).Input
+	})
+	mujica.FormItem(f, "password", &s.password, mujica.FormItemOptions[string]{Label: g.t("Password", "密码"), Required: true,
+		Validate: func(v string) string {
+			if len([]rune(v)) < 8 {
+				return g.t("Use at least 8 characters.", "至少 8 个字符。")
+			}
+			return ""
+		}}, func() *ui.Element {
+		r := mujica.PasswordInput(c, &s.password, mujica.PasswordInputOptions{})
+		if r.Submitted() {
+			s.st.Submit()
+		}
+		return r.Input
+	})
+	mujica.FormItem(f, "debut", &s.debut, mujica.FormItemOptions[mujica.Date]{Label: g.t("Debut date", "首演日期"), Required: true}, func() *ui.Element {
+		r := mujica.DatePicker(c, &s.debut, mujica.DatePickerOptions{Clearable: true})
+		if r.Changed() {
+			log("debut " + s.debut.Format("2006-01-02"))
+		}
+		return r.Element
+	})
+	mujica.FormItem(f, "roles", &s.tags, mujica.FormItemOptions[[]string]{Label: g.t("Roles", "担当"), Required: true,
+		Description: g.t("Up to 4; press Enter after each.", "最多 4 个；每个后按 Enter。")}, func() *ui.Element {
+		r := mujica.TagsInput(c, &s.tags, mujica.TagsInputOptions{Max: 4, Invalid: s.st.Error("roles") != "", Placeholder: g.t("keyboard, bass…", "键盘、贝斯…")})
+		if r.Changed() {
+			log(fmt.Sprintf("roles %q", s.tags))
+		}
+		return r.Input
+	})
+	mujica.FormItem(f, "terms", &s.terms, mujica.FormItemOptions[bool]{Label: g.t("Terms", "条款"),
+		Validate: func(v bool) string {
+			if !v {
+				return g.t("Accept the terms to continue.", "请先同意条款。")
+			}
+			return ""
+		}}, func() *ui.Element {
+		e := mujica.Checkbox(c, &s.terms, g.t("I accept the covenant of the masquerade", "我接受假面舞会的盟约"), mujica.CheckboxOptions{})
+		if e.Changed() {
+			log(fmt.Sprintf("terms %v", s.terms))
+		}
+		return e
+	})
+}
+
+func (g *gallery) formSuccess(c *ui.Context, log func(string)) {
+	s := &g.cForm
+	r := mujica.Result(c, mujica.ResultOptions{Kind: mujica.ResultSuccess, Title: g.t("Entry received", "报名已收到"),
+		Description: fmt.Sprintf(g.t("%s, your debut on %s is on the ledger.", "%s，你在 %s 的首演已登记。"), s.name, s.debut.Format("2006-01-02")),
+		Actions:     []string{g.t("New entry", "新的报名")}})
+	if r.Action == 0 {
+		*s = newFormSubmitDemo()
+		log("new entry")
+	}
+}
+
+func (g *gallery) formFailure(c *ui.Context, log func(string)) {
+	s := &g.cForm
+	r := mujica.Result(c, mujica.ResultOptions{Kind: mujica.ResultFailure, Title: g.t("Entry not sent", "报名未送达"), Description: s.failure,
+		Actions: []string{g.t("Retry", "重试"), g.t("Back to the form", "返回表单")}})
+	switch r.Action {
+	case 0:
+		s.phase = formEditing
+		s.st.Submit()
+		log("retry")
+	case 1:
+		s.phase = formEditing
+		log("back to the form")
+	}
+}
diff --git a/examples/gallery/composite_settings.go b/examples/gallery/composite_settings.go
new file mode 100644
index 0000000..3be957e
--- /dev/null
+++ b/examples/gallery/composite_settings.go
@@ -0,0 +1,212 @@
+package main
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/egoist/mygo/ui"
+
+	mujica "mujicaui"
+	"mujicaui/icons"
+)
+
+const settingsID = "c-settings"
+
+// settingsValues is one full set of preferences; drafts compare to saved ones with ==.
+type settingsValues struct {
+	workspace string
+	language  string
+	startPage string
+	launch    bool
+	theme     string
+	fontSize  float64
+	sidebar   float64
+	reduce    bool
+	telemetry bool
+	crashes   bool
+	history   float64
+	lock      string
+}
+
+var settingsInitial = settingsValues{
+	workspace: "Mujica", language: "en", startPage: "last", launch: true,
+	theme: "system", fontSize: 14, sidebar: 240,
+	crashes: true, history: 30, lock: "15",
+}
+
+type settingsDemo struct {
+	tab          int
+	saved, draft settingsValues
+}
+
+func newSettingsDemo() settingsDemo {
+	return settingsDemo{saved: settingsInitial, draft: settingsInitial}
+}
+
+func (g *gallery) settingsView(c *ui.Context, log func(string)) {
+	s := &g.cSettings
+	mujica.Card(c, mujica.CardOptions{Title: g.t("Preferences", "偏好设置"), Footer: func() { g.settingsFooter(c, log) }}, func() {
+		tabs := []mujica.Tab{
+			{Label: g.t("General", "通用"), Icon: icons.Must("settings"), Panel: func() { g.settingsGeneral(c, log) }},
+			{Label: g.t("Appearance", "外观"), Icon: icons.Must("palette"), Panel: func() { g.settingsAppearance(c, log) }},
+			{Label: g.t("Privacy", "隐私"), Icon: icons.Must("lock"), Panel: func() { g.settingsPrivacy(c, log) }},
+		}
+		if mujica.Tabs(c, &s.tab, tabs, mujica.TabsOptions{Label: g.t("Preference groups", "设置分组")}).Changed() {
+			log("tab " + tabs[s.tab].Label)
+		}
+	})
+}
+
+// settingsPanel lays one tab's fields in a readable column.
+func settingsPanel(c *ui.Context, fields func()) {
+	ui.Column(c).FillWidth().MaxWidth(560).Gap(20).Padding(16, 0, 4, 0).Children(fields)
+}
+
+// workspaceError checks the one free-text preference.
+func (g *gallery) workspaceError(name string) string {
+	if strings.TrimSpace(name) == "" {
+		return g.t("Name the workspace.", "请为工作区命名。")
+	}
+	return ""
+}
+
+func (g *gallery) settingsGeneral(c *ui.Context, log func(string)) {
+	d := &g.cSettings.draft
+	settingsPanel(c, func() {
+		bad := g.workspaceError(d.workspace)
+		mujica.FormField(c, g.t("Workspace name", "工作区名称"), mujica.FormFieldOptions{Required: true, Error: bad,
+			Description: g.t("Shown in the title bar.", "显示在标题栏中。")}, func() *ui.Element {
+			r := mujica.TextInput(c, &d.workspace, mujica.TextInputOptions{Error: bad})
+			if r.Changed() {
+				log(fmt.Sprintf("workspace %q", d.workspace))
+			}
+			return r.Input
+		})
+		mujica.FormField(c, g.t("Language", "语言"), mujica.FormFieldOptions{}, func() *ui.Element {
+			r := mujica.Select(c, &d.language, []mujica.SelectOption[string]{
+				{Value: "en", Label: "English"}, {Value: "zh", Label: "简体中文"}, {Value: "ja", Label: "日本語"},
+			}, mujica.SelectOptions{})
+			if r.Changed() {
+				log("language " + d.language)
+			}
+			return r.Element
+		})
+		mujica.FormField(c, g.t("On startup", "启动时"), mujica.FormFieldOptions{}, func() *ui.Element {
+			r := mujica.RadioGroup(c, &d.startPage, []mujica.RadioItem[string]{
+				{Value: "blank", Label: g.t("Open a blank page", "打开空白页")},
+				{Value: "last", Label: g.t("Reopen the last session", "恢复上次会话")},
+				{Value: "home", Label: g.t("Open the home page", "打开主页")},
+			}, mujica.RadioGroupOptions{})
+			if r.Changed() {
+				log("startup " + d.startPage)
+			}
+			return r.Element
+		})
+		mujica.FormField(c, g.t("Login item", "登录项"), mujica.FormFieldOptions{}, func() *ui.Element {
+			e := mujica.Switch(c, &d.launch, g.t("Launch at login", "登录时启动"), mujica.SwitchOptions{})
+			if e.Changed() {
+				log(fmt.Sprintf("launch at login %v", d.launch))
+			}
+			return e
+		})
+	})
+}
+
+func (g *gallery) settingsAppearance(c *ui.Context, log func(string)) {
+	d := &g.cSettings.draft
+	settingsPanel(c, func() {
+		mujica.FormField(c, g.t("Theme", "主题"), mujica.FormFieldOptions{}, func() *ui.Element {
+			r := mujica.RadioGroup(c, &d.theme, []mujica.RadioItem[string]{
+				{Value: "system", Label: g.t("System", "跟随系统")}, {Value: "light", Label: g.t("Light", "浅色")}, {Value: "dark", Label: g.t("Dark", "深色")},
+			}, mujica.RadioGroupOptions{Horizontal: true})
+			if r.Changed() {
+				log("theme " + d.theme)
+			}
+			return r.Element
+		})
+		mujica.FormField(c, g.t("Text size", "文字大小"), mujica.FormFieldOptions{}, func() *ui.Element {
+			r := mujica.Slider(c, &d.fontSize, mujica.SliderOptions{Min: 12, Max: 20, Step: 1, ShowValue: true,
+				Marks:  []mujica.SliderMark{{Value: 12, Label: "12"}, {Value: 16, Label: "16"}, {Value: 20, Label: "20"}},
+				Format: func(v float64) string { return fmt.Sprintf("%.0f pt", v) }})
+			if r.Changed() {
+				log(fmt.Sprintf("text size %.0f", d.fontSize))
+			}
+			return r.Element
+		})
+		mujica.FormField(c, g.t("Sidebar width", "侧栏宽度"), mujica.FormFieldOptions{Description: g.t("In DIPs, from 180 to 360.", "单位 DIP，180 至 360。")}, func() *ui.Element {
+			r := mujica.NumberInput(c, &d.sidebar, mujica.NumberInputOptions{Min: 180, Max: 360, Step: 10})
+			if r.Changed() {
+				log(fmt.Sprintf("sidebar width %.0f", d.sidebar))
+			}
+			return r.Input
+		})
+		mujica.FormField(c, g.t("Motion", "动效"), mujica.FormFieldOptions{}, func() *ui.Element {
+			e := mujica.Switch(c, &d.reduce, g.t("Reduce motion", "减少动效"), mujica.SwitchOptions{})
+			if e.Changed() {
+				log(fmt.Sprintf("reduce motion %v", d.reduce))
+			}
+			return e
+		})
+	})
+}
+
+func (g *gallery) settingsPrivacy(c *ui.Context, log func(string)) {
+	d := &g.cSettings.draft
+	settingsPanel(c, func() {
+		mujica.FormField(c, g.t("Usage data", "使用数据"), mujica.FormFieldOptions{Description: g.t("Nothing leaves this demo.", "本示例不会发送任何数据。")}, func() *ui.Element {
+			e := mujica.Switch(c, &d.telemetry, g.t("Share anonymous usage data", "共享匿名使用数据"), mujica.SwitchOptions{})
+			if e.Changed() {
+				log(fmt.Sprintf("usage data %v", d.telemetry))
+			}
+			return e
+		})
+		mujica.FormField(c, g.t("Crash reports", "崩溃报告"), mujica.FormFieldOptions{}, func() *ui.Element {
+			e := mujica.Switch(c, &d.crashes, g.t("Send crash reports", "发送崩溃报告"), mujica.SwitchOptions{})
+			if e.Changed() {
+				log(fmt.Sprintf("crash reports %v", d.crashes))
+			}
+			return e
+		})
+		mujica.FormField(c, g.t("Keep history", "保留历史"), mujica.FormFieldOptions{Description: g.t("Days, from 0 to 365; 0 keeps none.", "天数，0 至 365；0 表示不保留。")}, func() *ui.Element {
+			r := mujica.NumberInput(c, &d.history, mujica.NumberInputOptions{Min: 0, Max: 365, Step: 1})
+			if r.Changed() {
+				log(fmt.Sprintf("history %.0f days", d.history))
+			}
+			return r.Input
+		})
+		mujica.FormField(c, g.t("Lock after", "自动锁定"), mujica.FormFieldOptions{}, func() *ui.Element {
+			r := mujica.Select(c, &d.lock, []mujica.SelectOption[string]{
+				{Value: "never", Label: g.t("Never", "从不")}, {Value: "5", Label: g.t("5 minutes", "5 分钟")},
+				{Value: "15", Label: g.t("15 minutes", "15 分钟")}, {Value: "60", Label: g.t("1 hour", "1 小时")},
+			}, mujica.SelectOptions{})
+			if r.Changed() {
+				log("lock after " + d.lock)
+			}
+			return r.Element
+		})
+	})
+}
+
+// settingsFooter flags unsaved changes and holds Reset and Save.
+func (g *gallery) settingsFooter(c *ui.Context, log func(string)) {
+	s := &g.cSettings
+	dirty := s.draft != s.saved
+	invalid := g.workspaceError(s.draft.workspace) != ""
+	ui.Row(c).FillWidth().AlignItems(ui.Center).Gap(12).Children(func() {
+		if dirty {
+			mujica.StatusIndicator(c, mujica.StatusWarning, mujica.StatusIndicatorOptions{Label: g.t("Unsaved changes", "有未保存的更改")})
+		} else {
+			mujica.StatusIndicator(c, mujica.StatusSuccess, mujica.StatusIndicatorOptions{Label: g.t("All changes saved", "更改均已保存")})
+		}
+		ui.Box(c).Grow(1)
+		if mujica.Button(c, g.t("Reset", "重置"), mujica.ButtonOptions{Variant: mujica.Secondary, Disabled: s.draft == settingsInitial}).Clicked() {
+			s.draft = settingsInitial
+			log("reset to initial values")
+		}
+		if mujica.Button(c, g.t("Save", "保存"), mujica.ButtonOptions{Disabled: !dirty || invalid}).Clicked() {
+			s.saved = s.draft
+			log("saved")
+			mujica.ShowToast(c, mujica.ToastMessage{ID: "settings-saved", Severity: mujica.SeveritySuccess, Message: g.t("Settings saved", "设置已保存")})
+		}
+	})
+}
diff --git a/examples/gallery/composite_test.go b/examples/gallery/composite_test.go
new file mode 100644
index 0000000..4b2be4e
--- /dev/null
+++ b/examples/gallery/composite_test.go
@@ -0,0 +1,138 @@
+package main
+
+import (
+	"slices"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/egoist/mygo/ui"
+)
+
+// compositeTester opens the gallery on one composition at 1200×800.
+func compositeTester(id string) (*gallery, *ui.Tester) {
+	g := newGallery()
+	g.selected = id
+	return g, ui.NewTester(g.view, 1200, 800)
+}
+
+func click(t *testing.T, tt *ui.Tester, label string) {
+	t.Helper()
+	if err := tt.Click(label); err != nil {
+		t.Fatal(err)
+	}
+}
+
+// await renders frames until done holds or 5 seconds pass.
+func await(tt *ui.Tester, done func() bool) {
+	for deadline := time.Now().Add(5 * time.Second); !done() && time.Now().Before(deadline); {
+		time.Sleep(20 * time.Millisecond)
+		tt.Frame()
+	}
+}
+
+func TestCompositeSettingsSaveAndReset(t *testing.T) {
+	g, tt := compositeTester(settingsID)
+	s := &g.cSettings
+	click(t, tt, "Appearance")
+	click(t, tt, "Reduce motion")
+	if !s.draft.reduce || s.saved.reduce {
+		t.Fatalf("draft reduce %v, saved reduce %v", s.draft.reduce, s.saved.reduce)
+	}
+	if !tt.HasText("Unsaved changes") {
+		t.Fatalf("no unsaved flag in %q", tt.Texts())
+	}
+	click(t, tt, "Save")
+	if s.saved != s.draft || !s.saved.reduce {
+		t.Fatalf("saved %+v, draft %+v", s.saved, s.draft)
+	}
+	if !tt.HasText("Settings saved") || !tt.HasText("All changes saved") {
+		t.Fatalf("no saved toast in %q", tt.Texts())
+	}
+	click(t, tt, "Reset")
+	if s.draft != settingsInitial || !s.saved.reduce {
+		t.Fatalf("reset draft %+v, saved %+v", s.draft, s.saved)
+	}
+	if !tt.HasText("Unsaved changes") {
+		t.Fatal("reset away from the saved values is not flagged")
+	}
+}
+
+func TestCompositeFilesFilterSelectDelete(t *testing.T) {
+	g, tt := compositeTester(filesID)
+	s := &g.cFiles
+	click(t, tt, "Filter files")
+	tt.Type("rehearsal")
+	if s.query != "rehearsal" || s.table.Rows() != 1 {
+		t.Fatalf("query %q shows %d rows", s.query, s.table.Rows())
+	}
+	click(t, tt, "Select row")
+	if s.table.Selection.Len() != 1 || !s.table.Selection.Has(2) {
+		t.Fatalf("selection %v", slices.Collect(s.table.Selection.All()))
+	}
+	click(t, tt, "Delete")
+	if !s.deleting || !slices.Equal(s.doomed, []int{2}) {
+		t.Fatalf("deleting %v, doomed %v", s.deleting, s.doomed)
+	}
+	click(t, tt, "Delete permanently")
+	if len(s.entries) != 7 || slices.ContainsFunc(s.entries, func(f fileEntry) bool { return f.ID == 2 }) {
+		t.Fatalf("entries after delete %+v", s.entries)
+	}
+	if s.deleting || s.table.Selection.Len() != 0 {
+		t.Fatalf("deleting %v, selection %d", s.deleting, s.table.Selection.Len())
+	}
+	if !tt.HasText("Nothing matches “rehearsal”.") {
+		t.Fatalf("no empty search state in %q", tt.Texts())
+	}
+}
+
+func TestCompositeFormInvalidThenValid(t *testing.T) {
+	g, tt := compositeTester(formID)
+	s := &g.cForm
+	click(t, tt, "Submit entry")
+	if got := s.st.Error("name"); got != "Required" {
+		t.Fatalf("name error %q", got)
+	}
+	if got := s.st.Error("terms"); got != "Accept the terms to continue." {
+		t.Fatalf("terms error %q", got)
+	}
+	if !tt.Focused("Stage name") {
+		t.Fatal("the first invalid field has no focus")
+	}
+	tt.Type("Mortis")
+	click(t, tt, "Password")
+	tt.Type("hunter22secret")
+	click(t, tt, "Select date") // the date field itself; its FormItem label focuses the picker's column
+	tt.Type("2026-12-24")
+	tt.Key(0, ui.KeyEnter)
+	click(t, tt, "Roles")
+	tt.Type("guitar")
+	tt.Key(0, ui.KeyEnter)
+	click(t, tt, "I accept the covenant of the masquerade")
+	if s.name != "Mortis" || s.password != "hunter22secret" || s.debut.Format("2006-01-02") != "2026-12-24" ||
+		!slices.Equal(s.tags, []string{"guitar"}) || !s.terms {
+		t.Fatalf("values %q %q %v %q %v", s.name, s.password, s.debut, s.tags, s.terms)
+	}
+	click(t, tt, "Submit entry")
+	await(tt, s.st.Submitting) // the name check finishes first
+	if !s.st.Submitting() || !tt.HasText("Submitting…") {
+		t.Fatalf("no loading overlay in %q", tt.Texts())
+	}
+	click(t, tt, "Submit entry") // the overlay blocks a second submit
+	await(tt, func() bool { return s.phase == formSucceeded })
+	if s.phase != formSucceeded || !tt.HasText("Entry received") {
+		t.Fatalf("phase %d, texts %q", s.phase, tt.Texts())
+	}
+	submits := 0
+	for _, e := range g.events {
+		if strings.Contains(e.text, "hunter22secret") {
+			t.Fatalf("password logged: %q", e.text)
+		}
+		if e.page == formID && strings.HasPrefix(e.text, "submitted ") {
+			submits++
+		}
+	}
+	if submits != 1 {
+		t.Fatalf("%d submits, want 1", submits)
+	}
+}
diff --git a/examples/gallery/nav.go b/examples/gallery/nav.go
index 649106b..6101655 100644
--- a/examples/gallery/nav.go
+++ b/examples/gallery/nav.go
@@ -11,6 +11,26 @@ import (
 
 const overtureID = "overture"
 
+// composition is one PRD §8 demo that combines components.
+type composition struct {
+	ID, Name, ZhName, About, ZhAbout, Icon string
+}
+
+var compositions = []composition{
+	{settingsID, "Settings", "设置页", "Tabs of labelled controls with save, reset and an unsaved-changes flag.", "分页的带标签控件，可保存、重置，并标出未保存的更改。", "settings"},
+	{filesID, "File list", "文件列表", "Filter, select, rename and delete files; drop or pick files to add them.", "筛选、选择、重命名与删除文件；拖入或选取文件以添加。", "folder"},
+	{formID, "Form submission", "表单提交", "Validated fields, an async name check, a guarded submit and its result.", "带校验的字段、异步名称检查、防重复提交及其结果。", "file-text"},
+}
+
+func compositionOf(id string) composition {
+	for _, cp := range compositions {
+		if cp.ID == id {
+			return cp
+		}
+	}
+	panic("gallery: no composition " + id)
+}
+
 // categoryZh names each PRD group in Chinese.
 var categoryZh = map[string]string{
 	"Layout": "布局与桌面", "Display": "基础展示", "Inputs": "基础输入", "Choices": "选择控件",
@@ -47,6 +67,16 @@ func (g *gallery) sections() []mujica.SidebarSection {
 	out := []mujica.SidebarSection{{Title: g.t("Overture", "序章"), Items: []mujica.SidebarItem{
 		{ID: overtureID, Label: g.t("Overture", "序章"), Icon: icons.Must("house")},
 	}}}
+	var comps []mujica.SidebarItem
+	q := strings.ToLower(strings.TrimSpace(g.query))
+	for _, cp := range compositions {
+		if q == "" || strings.Contains(strings.ToLower(cp.ID+" "+cp.Name+" "+cp.ZhName), q) {
+			comps = append(comps, mujica.SidebarItem{ID: cp.ID, Label: g.t(cp.Name, cp.ZhName), Icon: icons.Must(cp.Icon)})
+		}
+	}
+	if len(comps) > 0 {
+		out = append(out, mujica.SidebarSection{Title: g.t("Compositions", "组合示例"), Items: comps})
+	}
 	index := map[string]int{}
 	for _, p := range g.pages {
 		if !matches(p, g.query) {
@@ -87,6 +117,10 @@ func (g *gallery) commandPalette(c *ui.Context) {
 		{ID: "density", Label: g.t("Cycle density", "切换密度"), Group: g.t("Window", "窗口"), Keywords: []string{"compact", "紧凑"}},
 		{ID: "locale", Label: g.t("Switch to Chinese", "切换到英文"), Group: g.t("Window", "窗口"), Keywords: []string{"language", "语言"}},
 	}
+	for _, cp := range compositions {
+		cmds = append(cmds, mujica.Command{ID: "page:" + cp.ID, Label: g.t(cp.Name, cp.ZhName), Group: g.t("Compositions", "组合示例"),
+			Keywords: []string{cp.Name, cp.ZhName, "composition", "组合"}})
+	}
 	for _, p := range g.pages {
 		cmds = append(cmds, mujica.Command{ID: "page:" + p.ID, Label: p.ID + " " + g.pageName(p), Group: g.categoryName(p.Category),
 			Keywords: []string{p.Name, p.ZhName, p.Category, categoryZh[p.Category]}})
diff --git a/examples/gallery/page_view.go b/examples/gallery/page_view.go
index e9b1d04..105cc96 100644
--- a/examples/gallery/page_view.go
+++ b/examples/gallery/page_view.go
@@ -60,3 +60,15 @@ func (g *gallery) eventCard(c *ui.Context, id string) {
 		}
 	})
 }
+
+// compositePage shows one composition demo above its events.
+func (g *gallery) compositePage(c *ui.Context, id string, body func(c *ui.Context, log func(string))) {
+	cp := compositionOf(id)
+	mujica.Container(c, mujica.ContainerOptions{MaxWidth: 1080, Center: true}, func() {
+		ui.Column(c).FillWidth().Gap(24).Children(func() {
+			mujica.Heading(c, g.t(cp.Name, cp.ZhName), mujica.HeadingOptions{Subtitle: g.t(cp.About, cp.ZhAbout), Divider: true})
+			ui.Column(c).FillWidth().Gap(16).Children(func() { body(c, g.logFor(id)) })
+			g.eventCard(c, id)
+		})
+	})
+}