Bottom sheet

Category: Containment
Tokens: comp.bottom-sheet
Level: Composed
Built from: Modal layer

Overview

Web: tanrei-bottom-sheet; schedule
SwiftUI: tanreiBottomSheet; schedule
Jetpack Compose: TanreiBottomSheet; schedule
Flutter: TanreiBottomSheet; schedule
React Native: BottomSheet; schedule

Generated from docs/status/status.json, specs/bottom-sheet.spec.json

A modal sheet: open it with the button

Save photo

Usage

A bottom sheet is controlled, and it never closes itself. You open it by setting open. When the person asks it to go, the sheet emits close with the reason, and you set open back to false. SwiftUI is the one exception: there open is a binding, so the sheet writes false to it and then calls onClose. If you leave open true, the sheet stays, and after a drag it settles back at its lowest height. On the web this differs from the dialog: the sheet cancels the native cancel event and emits close in its place, so Escape does not close it until you do.

close carries one of five reasons, in the platform’s casing:

Reason	What the person did	Which form
`close`	Pressed the sheet’s close button (`closable`)	Standard and modal
`drag`	Released a drag below half of the sheet’s lowest height, or flung it down from there	Standard and modal
`scrim`	Pressed the dim area around a modal sheet	Modal
`escape`	Pressed Escape	Modal
`back`	Used the platform’s back: Android’s back button or gesture, the iOS accessibility escape gesture. On the web, a close request that comes without a key, such as Android’s back gesture in the browser, is `back`.	Modal

The sheet emits close only while dismissible is true, and exactly once for each request. While it is false, the scrim, Escape and back do nothing, and a drag down settles at the lowest height. The close button is the exception: it asks with the reason close whatever dismissible says, because it is a way out you chose to draw.

The sheet has two forms on variant. Modal, the default, is a modal overlay: it dims the whole window, keeps focus inside, and returns focus when it closes. Standard is a layout region, not an overlay: it covers the bottom of the parent you place it in, draws no scrim, and lets the person keep working in the content above it.

What goes in the sheet is yours. The sheet insets its content by its padding (set inset to false for a list whose rows pad themselves), clips it, hands it a content color and scrolls it. Give it a headline and it draws a header above the content: the headline, a heading that also names the sheet where label is empty, and, with closable on, a close button named by closeLabel — a small Button, tonal in the default system, as every close button in Tanrei is. A divider stands below the header as dividerVisibility says, and the header stays in place while the content scrolls. closable is off by default, because the handle and, for a modal sheet, the scrim are the sheet’s ways out; turn it on for a standard sheet or a sheet without a handle.

Mark the element that should get focus when the sheet opens with the platform’s own mark: autofocus on the web, .defaultFocus or an @AccessibilityFocusState on SwiftUI, a FocusRequester passed as initialFocus on Compose, autofocus: true on Flutter, and initialFocusRef on React Native. Without a mark, focus goes to the sheet itself, so its label is read first.

<tanrei-button id="save" variant="outlined">Save photo</tanrei-button>

<!-- Modal is the default. closedby="none" is dismissible set to false. -->
<tanrei-bottom-sheet id="save-sheet" label="Save photo" handle-label="Resize sheet">
  <p>Choose where to save the photo.</p>
  <tanrei-button variant="text" autofocus>Done</tanrei-button>
</tanrei-bottom-sheet>

<!-- Standard: covers the bottom of its containing block. flush is inset set to false; no-handle is handle set to false. -->
<div class="map" style="position: relative">
  <tanrei-bottom-sheet variant="standard" open label="Nearby places" handle-label="Resize sheet" flush>
    <tanrei-list>…</tanrei-list>
  </tanrei-bottom-sheet>
</div>

<script type="module">
  import '@tanrei/web/components/bottom-sheet';
  const sheet = document.querySelector('#save-sheet');
  document.querySelector('#save').addEventListener('click', () => (sheet.open = true));
  sheet.querySelector('tanrei-button').addEventListener('click', () => (sheet.open = false));
  // The sheet never closes itself. detail.reason is drag, scrim, escape or back.
  sheet.addEventListener('close', (e) => (sheet.open = false));
  // The person moved it to its other height. The sheet has already set detent.
  sheet.addEventListener('detentchange', (e) => console.log(e.detail.detent));
</script>

import { BottomSheet, Button } from '@tanrei/react';

<BottomSheet
  open={open}
  label="Save photo"
  handleLabel="Resize sheet"
  onClose={() => setOpen(false)}
  onDetentChange={(e) => setDetent(e.detail.detent)}
>
  <p>Choose where to save the photo.</p>
  <Button variant="text" onClick={() => setOpen(false)}>Done</Button>
</BottomSheet>

import Tanrei

// A modifier on the view the sheet covers, as .sheet is. Closing writes false to the binding,
// then calls onClose with the reason. A height the person chooses is written to detent.
PhotoView(photo)
    .tanreiBottomSheet(isPresented: $saving, detent: $detent,
                       handleLabel: "Resize sheet", label: "Save photo") {
        SaveTargets(photo)
        TanreiButton("Done", variant: .text) { saving = false }
    }

// Standard: an overlay at the bottom of the view it covers.
MapView()
    .tanreiBottomSheet(isPresented: $placesShown, variant: .standard,
                       handleLabel: "Resize sheet", label: "Nearby places") {
        PlacesList()
    }

import io.github.chnotchy.tanrei.components.TanreiBottomSheet
import io.github.chnotchy.tanrei.components.TanreiButton
import io.github.chnotchy.tanrei.tokens.TanreiButtonVariant

// visible rather than calling it only while open, so that the exit motion can run.
// Set it to false from onClose, which receives the reason.
TanreiBottomSheet(
    visible = saving,
    onClose = { saving = false },
    detent = detent,
    onDetentChange = { detent = it },
    handleLabel = "Resize sheet",
    contentDescription = "Save photo",
) {
    SaveTargets(photo)
    TanreiButton(text = "Done", onClick = { saving = false }, variant = TanreiButtonVariant.Text)
}

import 'package:tanrei/tanrei.dart';

// A modal sheet is the last child of a Stack over the whole page. Set open to false from onClose.
Stack(
  children: <Widget>[
    const Positioned.fill(child: PhotoPage()),
    TanreiBottomSheet(
      open: saving,
      onClose: (TanreiSheetCloseReason reason) => setState(() => saving = false),
      detent: detent,
      onDetentChanged: (value) => setState(() => detent = value),
      handleSemanticLabel: 'Resize sheet',
      semanticLabel: 'Save photo',
      child: const SaveTargets(),
    ),
  ],
),

import { useRef, useState } from 'react';
import type { View } from 'react-native';
import { BottomSheet, Button } from '@tanrei/react-native';

const done = useRef<View>(null);
const [open, setOpen] = useState(false);

// Controlled: set open to false from onClose, which receives the reason ('drag', 'scrim', 'escape' or 'back').
// A modal sheet is presented in a transparent Modal. The sheet's insets prop replaces the sides of TanreiProvider's insets it names.
<BottomSheet
  open={open}
  onClose={(reason) => setOpen(false)}
  detent={detent}
  onDetentChange={setDetent}
  handleLabel="Resize sheet"
  accessibilityLabel="Save photo"
  initialFocusRef={done}
>
  <SaveTargets />
  <Button ref={done} variant="text" onPress={() => setOpen(false)}>Done</Button>
</BottomSheet>

Specs

A standard sheet over the bottom of its parent: drag it down to close it

Map

Show nearby places

Three cafés and a bakery are open within a ten-minute walk.

Anatomy

Part	Description
1 `scrim` · optional	The modal layer's scrim over everything behind a modal sheet (MDL-1). It blocks presses and, while the sheet is dismissible, a press on it asks the sheet to close. A standard sheet draws none.
2 `container`	The raised surface docked to the bottom edge of the area it covers, centred and no wider than its maximum width, its top corners rounded and its bottom corners square. Its color reaches under the bottom system inset.
3 `drag-handle` · optional	The control at the top of the sheet: a Handle without a value, always drawn, that carries hover, focus and press on its box, with the grip centred in it. Activating it moves the sheet between its two heights.
4 `drag-handle.grip` · optional	The Handle's line: the short rounded bar drawn in the handle's box that says the sheet can be dragged.
5 `header` · optional	The row below the drag handle's row (or at the top without one) that holds the headline and the close button. Drawn while headline is not empty or closable is true; it stays in place while the content scrolls.
6 `headline` · optional	What the sheet is about ("Share photo"), a heading. It names the sheet where label is empty.
7 `close-button` · optional	An icon-only Button of the small size showing the close glyph at the end of the header, in the variant comp.bottom-sheet.close-button.variant names (tonal in the default system), as every host's close button is. The sheet places it and chooses its variant; everything else it reads from Button's own tokens.
8 `divider` · optional	A hairline across the sheet below the header: drawn whenever the header is in the default system, or only while the content is scrolled away from its top under dividerVisibility scroll.
9 `content`	Whatever the product puts in the sheet: a list of choices, a form, details. The sheet insets it (unless inset is false), clips it, hands it a content color and scrolls it; it does not lay it out.
10 `focus-ring` · optional	Gap-then-ring indicator around the drag handle's box, shown for keyboard focus.

Properties

Property	Type	Default	Description
`variant`	`standard` \| `modal`	`"modal"`	Standard sits over the lower part of the content while the content above stays usable (a layout region); modal dims and blocks everything else and holds focus until it closes (a modal overlay). Both read the same container tokens: the scrim and the behaviour set them apart. Not a token axis.
`open`	`boolean`	`false`	Whether the sheet is shown. The product opens it, and closes it in answer to close (or from its own controls); on SwiftUI, where it is a binding, the sheet writes false itself.
`detent`	`partial` \| `full`	`"partial"`	The height the sheet rests at while its content is taller than it: partial takes comp.bottom-sheet.container.partial-fraction of the area; full reaches up to comp.bottom-sheet.container.margin-block-start below the area's top. A sheet whose content is shorter than its partial height has one height, and detent changes nothing. The person moves between the two by dragging or with the drag handle (detentChange).
`dismissible`	`boolean`	`true`	Whether a drag below the sheet's lowest height asks it to close and, for a modal sheet, whether Escape, the platform's back and a press on the scrim do too. Set it to false only when the person must finish the sheet's task with one of its own controls.
`handle`	`boolean`	`true`	Draws the drag handle at the top of the sheet. Without it the sheet can still be dragged by its padding and content (BSH-9), but a keyboard or switch user has no way to change its height, so leave it on for a sheet whose content can be taller than its partial height.
`handleLabel`	`string`	`""`	The drag handle's accessible name ("Resize sheet"); its expanded state is exposed with it. Required while the handle is interactive (BSH-11).
`inset`	`boolean`	`true`	Insets the content by comp.bottom-sheet.container.padding. Set it to false for content that pads itself or reaches the edges (a list whose rows carry their own padding).
`label`	`string`	`""`	Names the sheet for assistive technology ("Share photo"): the modal dialog, or the standard sheet's region. Required unless headline names it.
`headline`	`string`	`""`	What the sheet is about ("Share photo"), drawn in its header (BSH-28). While label is empty it is the sheet's accessible name.
`closable`	`boolean`	`false`	Draws the close button at the end of the header (BSH-29). False by default: the drag handle and, for a modal sheet, the scrim are the sheet's ways out. Set it where a person who cannot drag needs one they can see — a standard sheet, or a sheet without a handle.
`closeLabel`	`string`	`""`	The close button's accessible name ("Close sharing"). Required while closable is true.
`dividerVisibility`	`auto` \| `always` \| `scroll`	`"auto"`	When the divider below the header is drawn. always: whenever the header is drawn, at rest as well as while the content is scrolled. scroll: only while the content is scrolled away from its top. auto takes comp.bottom-sheet.divider.visibility, the design system's answer (always in the default system).

Slots

Slot	Description
`default`	The content. A fixture's content string is plain text, which takes sys.typescale.body in the content color (BSH-8).

Events

Event	Description
`close`	The sheet asks to be closed: its close button (BSH-29), a released drag below its lowest height, or for a modal sheet a press on the scrim, Escape or the platform's back. Carries which of these it was, named close, drag, scrim, escape or back (in the platform's casing). The close button asks whatever dismissible says; the others only while dismissible is true.
`detentChange`	The person moved the sheet to its other height, by a drag or with the drag handle. Carries the new detent (partial or full). Not emitted when the product sets detent.

States

Behavior

Requirements in EARS form. Every platform implementation is tested against these ids.

ID	Requirement
`BSH-1`	WHEN open becomes true THE bottom sheet SHALL slide its container up from below the bottom edge of the area it covers to its height (BSH-6) — WHILE variant is modal over the whole window on its modal layer, fading the layer's scrim in comp.bottom-sheet.scrim.color and comp.bottom-sheet.scrim.blur in behind it in step (MDL-1, MDL-7); WHILE variant is standard over the bottom of the parent the product placed it in, with no scrim — over comp.bottom-sheet.motion.enter-duration with comp.bottom-sheet.motion.enter-easing; WHEN open becomes false THE bottom sheet SHALL slide it down out of view from wherever it is and fade the scrim out, over comp.bottom-sheet.motion.exit-duration with comp.bottom-sheet.motion.exit-easing. WHERE motion is reduced it SHALL fade in and out in place without sliding, or appear and disappear at once on a platform whose reduced-motion setting removes every animation (Android's). A sheet that is mounted with open true SHALL appear in place without motion.
`BSH-2`	WHILE variant is modal and the sheet is open THE bottom sheet SHALL make everything outside it inert, keep the content behind it from scrolling and keep focus inside it, as its modal layer does (MDL-2, MDL-4): a modal overlay.
`BSH-3`	WHEN open changes from false to true THE bottom sheet SHALL move focus to the element in it that the product marked for initial focus (the platform's own mark, named in the platform notes) or, without one, to its container, so that assistive technology reads its label first; WHEN it closes while focus is inside it THE bottom sheet SHALL return focus to the element that had it when the sheet opened or, where that element no longer exists or cannot take focus, to the platform's default for a closed overlay. Focus SHALL move when the sheet opens or closes, not when its motion ends. This holds for both variants (a modal sheet moves and returns focus as its modal layer does, MDL-3, MDL-5); a standard sheet mounted with open true SHALL NOT move focus, and a modal sheet mounted with open true SHALL move focus in as if it had just opened, because it makes everything behind it unfocusable and focus must be somewhere it can reach.
`BSH-4`	WHILE variant is standard THE bottom sheet SHALL draw no scrim, SHALL NOT make anything inert, SHALL NOT keep focus inside it, SHALL let Tab and Shift+Tab move focus between it and the content it covers without closing it, and SHALL ignore Escape and the platform's back: a standard sheet is a layout region, not an overlay. The product places it over the content it covers, in a parent that holds both; the sheet SHALL dock to that parent's bottom edge, SHALL NOT resize or pad the content, and SHALL let presses on the part of the parent above it reach the content.
`BSH-5`	WHILE dismissible is true, WHEN the user presses the scrim, presses Escape or uses the platform's back WHILE variant is modal, as its modal layer answers them (MDL-6), or releases a drag that asks to close (BSH-9) in either variant, THE bottom sheet SHALL emit close exactly once with the reason scrim, escape, back or drag, and SHALL then be closed: through its binding where open is one (SwiftUI), and by the product setting open to false where open is a plain value (web, Compose, Flutter, React Native). WHILE dismissible is false THE bottom sheet SHALL ignore these inputs and emit nothing for them (its close button, BSH-29, still asks); a press on the scrim SHALL still reach nothing behind it.
`BSH-6`	THE bottom sheet SHALL be as tall as its drag handle's row, its header (BSH-28) and its content (with its insets), but no taller than its detent allows: WHILE detent is partial, comp.bottom-sheet.container.partial-fraction of the height of the area it covers; WHILE detent is full, that height less comp.bottom-sheet.container.margin-block-start. The area is the window below its top system inset for a modal sheet, and the parent the product placed it in for a standard sheet; WHILE the on-screen keyboard is shown the area SHALL end at the keyboard's top edge, so that the sheet sits on the keyboard and both heights are taken from the smaller area. The sheet has two heights only WHILE its content is taller than its partial height; otherwise it has one, and detent changes nothing.
`BSH-7`	THE bottom sheet SHALL draw its container at the bottom edge of the area, as wide as the area but no wider than comp.bottom-sheet.container.max-width and centred in it, filled with comp.bottom-sheet.container.color, raised by comp.bottom-sheet.container.elevation, with its top corners rounded by comp.bottom-sheet.container.shape and its bottom corners square; it SHALL extend its color under the bottom system inset and keep its content above that inset, and WHILE the on-screen keyboard is shown it SHALL sit on the keyboard (BSH-6) with its content above it.
`BSH-8`	THE bottom sheet SHALL lay out, top to bottom, the drag handle's row WHILE handle is true (BSH-12), the header WHILE there is one (BSH-28) and then its content. WHILE inset is true it SHALL inset the content by comp.bottom-sheet.container.padding from its start, end and bottom edges, and from its top edge WHILE handle is false and no header is drawn; WHILE inset is false the content SHALL reach the container's edges, below the handle's row and the header. It SHALL clip the content to the container's shape, SHALL hand it comp.bottom-sheet.content.color as the platform's inherited foreground (the web's inherited color, SwiftUI's foreground style, Compose's content color, Flutter's default text and icon style, React Native's Tanrei text context), and plain text given as content, where the platform must style it, SHALL take sys.typescale.body.
`BSH-9`	WHEN the user drags the sheet vertically — by its handle's row, by the padding around its content, or by its content where BSH-10 lets the drag reach the sheet — beyond the platform's touch slop THE bottom sheet SHALL follow the finger or pointer, never above its full height; WHEN the drag is released it SHALL settle at the next height in the direction of a fling, or else at the height nearest to where it was released, over comp.bottom-sheet.motion.enter-duration with comp.bottom-sheet.motion.enter-easing (at once where motion is reduced). A release below half of the sheet's lowest height, or a downward fling from its lowest height, SHALL ask to close WHILE dismissible is true (BSH-5, BSH-20); WHILE dismissible is false the sheet SHALL settle at its lowest height instead. A fling is a release faster than the platform's minimum fling velocity (Android's ViewConfiguration.getScaledMinimumFlingVelocity, Flutter's kMinFlingVelocity) or, where the platform names none (the web, SwiftUI, React Native), 0.5 points per millisecond; the touch slop is the platform's own (Android's ViewConfiguration.getScaledTouchSlop, Flutter's kTouchSlop) or, where the platform names none, 8 points. A release's velocity is the pointer's over its last moves: WHERE the pointer has not moved for longer than the time after which the platform's velocity tracker takes a pointer as stopped (40 milliseconds in Android's VelocityTracker, Jetpack Compose's VelocityTracker and Flutter's VelocityTracker) or, where the platform names none (the web, SwiftUI, React Native), 40 milliseconds before the release THE bottom sheet SHALL take the release as having no velocity, so that a drag that stops where it is wanted and is let go there is no fling, however fast it moved before it stopped. WHEN a drag ends at the height it did not start from THE bottom sheet SHALL set detent to it and emit detentChange exactly once with it.
`BSH-10`	WHILE the content is taller than the room the sheet gives it THE bottom sheet SHALL scroll the content inside the container, below the handle's row, and SHALL let assistive technology and keyboard focus scroll it at either height; a drag upward on the content SHALL first raise the sheet to its full height and then scroll the content, and a drag downward on the content SHALL first scroll the content to its top and then lower the sheet.
`BSH-11`	WHILE handle is true and the sheet has two heights THE bottom sheet SHALL make the drag handle one focus stop, a button named by handleLabel with the expanded state, true WHILE detent is full (its label and expanded, HDL-8), and WHEN the user activates it by pointer, touch, Enter or Space (its activate, HDL-7) THE bottom sheet SHALL move to its other height as BSH-9 settles and emit detentChange exactly once with the new detent; WHILE the sheet has one height the handle SHALL still be drawn at rest but SHALL NOT be focusable, pressable or exposed to assistive technology. WHILE the handle is interactive and handleLabel is empty it SHALL still render, and in debug builds report that the handle has no accessible name.
`BSH-12`	WHILE handle is true THE bottom sheet SHALL draw at its top a row holding the drag handle — a Handle of axis vertical and size medium, with no value and revealed — centred across the sheet with comp.bottom-sheet.handle.margin-block above and below it, and SHALL give that Handle its own tokens in place of the Handle's: the box comp.bottom-sheet.handle.container-width wide and comp.bottom-sheet.handle.container-height high with comp.bottom-sheet.handle.container-shape corners (HDL-3), the grip — the Handle's line — comp.bottom-sheet.handle.grip-width long and comp.bottom-sheet.handle.grip-height thick (HDL-1), and the container, line and state-layer colors of each state from the drag-handle control (comp.bottom-sheet.drag-handle.container.color, comp.bottom-sheet.drag-handle.grip.color, comp.bottom-sheet.drag-handle.state-layer.color, and so on for each state), its opacity in each state, and comp.bottom-sheet.motion.state-duration, comp.bottom-sheet.motion.state-easing and comp.bottom-sheet.motion.feedback-duration as its motion; in the default system each of them aliases the Handle's own. The row SHALL stay in place while the content scrolls.
`BSH-13`	WHILE the drag handle is hovered, keyboard-focused or pressed THE bottom sheet SHALL render the handle's box, grip and opacity from the component tokens of the highest-precedence active state, with precedence pressed over focused over hovered, and the grip at the Handle's length and thickness of a handle in use (HDL-4); focus gained by pointer or touch SHALL NOT select the focused state. A drag that starts on the handle SHALL keep it pressed while the sheet follows the drag, as a Handle is held for as long as a drag lasts (HDL-11).
`BSH-14`	WHEN the drag handle receives keyboard focus THE bottom sheet SHALL show the focus ring around the handle's box without animation; focus gained by pointer or touch SHALL NOT show it.
`BSH-15`	THE bottom sheet SHALL give the drag handle the Handle's hit area (HDL-5): at least sys.target.touch wide and high for touch input and sys.target.pointer for fine pointers, centred on its box, without changing its drawn size, and the Handle's vertical resize cursor; a platform that cannot tell the input type SHALL use sys.target.touch. A press on the rest of the handle's row drags the sheet as BSH-9 says.
`BSH-16`	WHEN the drag handle is pressed by pointer, touch, Enter or Space THE drag handle SHALL show the pressed state without delay and SHALL keep it visible for at least sys.motion.duration.press-hold, even when the press ends sooner (HDL-11).
`BSH-17`	WHILE pressed THE drag handle SHALL answer as sys.behavior.pressed-feedback names: overlay applies the pressed tokens to the whole container at once; ripple grows the pressed state layer from the point of contact (from the center for keyboard activation); dim applies the pressed opacity to the whole control and draws no state layer; none draws no answer to the press. Under ripple and dim only the container color stays with the state under the press; grip and opacity still come from the pressed tokens. Under none every part stays with the state under the press. The ripple grows over comp.bottom-sheet.motion.feedback-duration with comp.bottom-sheet.motion.state-easing, fades over comp.bottom-sheet.motion.state-duration with comp.bottom-sheet.motion.state-easing once the press has ended and press-hold has passed, and appears whole where motion is reduced.
`BSH-18`	THE bottom sheet SHALL ease its container's top corners and the drag handle's box corners by sys.shape.corner-smoothing (0 is a quarter circle, 0.6 the iOS continuous corner; a platform with only the OS curve draws it for any amount above 0) and show the handle's keyboard focus as sys.behavior.focus-style names (ring or glow); a platform that cannot draw a choice SHALL fall back to the first value and state that in its README.
`BSH-19`	WHEN the drag handle's colors, or its grip's length and thickness, change between states THE bottom sheet SHALL animate them over comp.bottom-sheet.motion.state-duration with comp.bottom-sheet.motion.state-easing, and SHALL change them at once where motion is reduced.
`BSH-20`	WHEN a released drag asks to close THE bottom sheet SHALL emit close (BSH-5), hold where the drag left it for one frame, and then slide out from there as BSH-1 says IF open has become false, or settle back at its lowest height as BSH-9 says IF open is still true (the product declined to close it).
`BSH-21`	WHEN the product changes detent while the sheet is open THE bottom sheet SHALL move to the new height over comp.bottom-sheet.motion.enter-duration with comp.bottom-sheet.motion.enter-easing (at once where motion is reduced) and SHALL NOT emit detentChange; where detent is a plain value (web, Compose, Flutter, React Native), a height the person chose (BSH-9, BSH-11) SHALL stay until the product sets detent again, and where it is a binding (SwiftUI) the sheet SHALL write the new detent to it.
`BSH-22`	THE bottom sheet SHALL expose its container, WHILE variant is modal, as a modal dialog named by label and, WHILE variant is standard, as a region named by label (a landmark on the web) — by the headline WHILE label is empty (BSH-28); WHILE label and headline are both empty it SHALL still render, and in debug builds report that it has no accessible name. The drag handle's grip, the Handle's line, SHALL be hidden from assistive technology; the handle itself is exposed only as BSH-11 says.
`BSH-23`	WHEN a dialog, a menu or another modal sheet opens from a modal bottom sheet THE bottom sheet SHALL stay below it, become inert with the rest of the window, and on the other overlay's closing receive back the focus that overlay returns, as its modal layer does (MDL-8, MDL-9); Escape SHALL dismiss only the topmost overlay.
`BSH-24`	WHILE the text size is enlarged THE bottom sheet SHALL grow with its content up to the height its detent allows and scroll the content beyond it (BSH-10), grow its header with a headline that wraps, and SHALL NOT scale the drag handle, nor the close button beyond what the Button itself does.
`BSH-25`	WHEN variant or detent names a value the bottom sheet does not define THE bottom sheet SHALL render with the default value, and in debug builds report the unknown value.
`BSH-26`	WHEN the layout direction is right-to-left THE bottom sheet SHALL keep its container and its drag handle centred, and its content SHALL follow the layout direction.
`BSH-27`	THE bottom sheet SHALL take its layout direction from where it is used — the direction of the nearest ancestor that sets one, and the platform's own where none does — and SHALL have no direction setting of its own; WHEN that direction changes while the bottom sheet is shown THE bottom sheet SHALL draw itself for the new direction at once, without a motion of its own, keeping its open state, its height and its focus.
`BSH-28`	WHILE headline is not empty or closable is true THE bottom sheet SHALL draw a header below the drag handle's row (or at the top of the container without one): a row at least comp.bottom-sheet.header.height high holding the headline from comp.bottom-sheet.container.padding after the start edge, in comp.bottom-sheet.headline.typescale and comp.bottom-sheet.headline.color, wrapping onto more lines rather than truncating and growing the row with it, exposed as a heading, and, WHILE closable is true, the close button ending comp.bottom-sheet.header.padding-inline-end before the end edge and comp.bottom-sheet.header.gap after the headline, both centred in the row; below it, a divider comp.bottom-sheet.divider.width thick in comp.bottom-sheet.divider.color across the sheet's full width WHILE dividerVisibility (or, for auto, comp.bottom-sheet.divider.visibility) is always, or is scroll and the content is scrolled away from its top, shown and hidden at once. The header SHALL NOT scroll with the content, and a drag on it SHALL move the sheet as a drag on the handle's row does (BSH-9). WHILE headline is not empty it SHALL name the sheet where label is empty. A dividerVisibility the sheet does not define SHALL be drawn as auto, and reported in debug builds.
`BSH-29`	WHILE closable is true THE bottom sheet SHALL draw its close button as an icon-only Button of the small size showing the glyph close of the system's icon set and named by closeLabel, in the variant comp.bottom-sheet.close-button.variant names, given through the channel a Button reads from the component that places it, and otherwise unrestyled: it reads Button's own tokens, answers hover, focus and press as any Button does and keeps its own minimum target (BTN-5); WHEN the user activates it THE bottom sheet SHALL emit close exactly once with the reason close, in either variant and whatever dismissible says, and SHALL then be closed as BSH-5 says. WHILE closable is true and closeLabel is empty it SHALL still draw the button, and in debug builds report that the button has no accessible name. THE bottom sheet SHALL draw no close mark of its own.
`BSH-30`	WHILE handle is false, dismissible is true and closable is false THE bottom sheet SHALL still render, and in debug builds report that it shows no way out a person can see: a drag, Escape and the scrim still close it, but nothing on screen says so to a person who cannot drag.
`BSH-31`	WHERE the platform has ARIA attributes (the web), WHEN the product sets an aria- attribute on the host, by the attribute or by the ARIA property that reflects it, THE bottom sheet SHALL move it to the data-aria- attribute of the same name, so that the host is no second node with its name, description or state, and SHALL expose it on its container (BSH-22) — its dialog WHILE variant is modal, its region otherwise — an id reference by the elements it names in the host's tree or a tree around it, a description after its own. WHILE label or headline is not empty it is the container's name (BSH-22), over a name given so; WHILE both are empty, a name given so is the container's name and SHALL NOT be reported as having none in debug builds. WHEN the product removes the aria- attribute or its data-aria- twin, or sets the ARIA property that reflects it (ariaLabel, ariaDescribedByElements…) to null, THE bottom sheet SHALL take it off that element.

Platform name mapping

Parity does not mean identical APIs. Each platform uses its own idiom for the same contract.

Spec	Web	SwiftUI	Jetpack Compose	Flutter	React Native
Component	`tanrei-bottom-sheet`	`tanreiBottomSheet`	`TanreiBottomSheet`	`TanreiBottomSheet`	`BottomSheet`
`variant` · Property	`variant`	`variant`	`variant`	`variant`	`variant`
`open` · Property	`open`	`isPresented`	`visible`	`open`	`open`
`detent` · Property	`detent`	`detent`	`detent`	`detent`	`detent`
`dismissible` · Property	`closedby`	`dismissible`	`dismissible`	`dismissible`	`dismissible`
`handle` · Property	`handle`	`handle`	`handle`	`showHandle`	`handle`
`handleLabel` · Property	`handleLabel`	`handleLabel`	`handleLabel`	`handleSemanticLabel`	`handleLabel`
`inset` · Property	`inset`	`inset`	`inset`	`inset`	`inset`
`label` · Property	`label`	`label`	`contentDescription`	`semanticLabel`	`accessibilityLabel`
`headline` · Property	`headline`	`headline`	`headline`	`headline`	`headline`
`closable` · Property	`closable`	`closable`	`closable`	`showCloseButton`	`closable`
`closeLabel` · Property	`closeLabel`	`closeLabel`	`closeLabel`	`closeButtonSemanticLabel`	`closeLabel`
`dividerVisibility` · Property	`dividerVisibility`	`dividerVisibility`	`dividerVisibility`	`dividerVisibility`	`dividerVisibility`
`close` · Event	`close`	`onClose`	`onClose`	`onClose`	`onClose`
`detentChange` · Event	`detentchange`	`detent`	`onDetentChange`	`onDetentChanged`	`onDetentChange`
Notes	`dismissible` is HTML's own `closedby` attribute, as on `<tanrei-dialog>`: `any` (the default) or `none`. `handle` and `inset` are boolean properties that default to true; their attributes are the inverses `no-handle` and `flush` (an HTML boolean attribute cannot default to true). `handleLabel` is the `handle-label` attribute, `closeLabel` the `close-label` attribute and `dividerVisibility` the `divider-visibility` attribute (`auto` reads `--tanrei-comp-bottom-sheet-divider-visibility` from the cascade with a style query, and where the browser has none the sheet writes the name it read on its header when it renders). The close button is a `<tanrei-button>` in the shadow root, icon-only (the close glyph in its `icon` slot, its `label` from `close-label`), whose variant comes from the resolved comp.bottom-sheet.close-button.variant through the internal channel a Button reads from its host; the headline is an `<h2>`. `close` is a CustomEvent whose `detail.reason` is `close`, `drag`, `scrim`, `escape` or `back` (`back` when a modal sheet's native `cancel` arrives without an Escape key, as Android's back gesture sends it), and `detentchange` one whose `detail.detent` is the new detent; the element sets `detent` itself before firing it. The product sets `open` to false from `close`. The content is the default slot. Drags use pointer events with `touch-action: none` on the handle's row and the top edge; the content scrolls natively and hands the drag over at its top (BSH-10). Fling 0.5 px/ms, slop 8 px. Insets are `env(safe-area-inset-bottom)`; the on-screen keyboard is read from `visualViewport`. Snapshot harness: a 400 × 720 viewport with a `surface` page; the sheet opened by `open`; the screenshot is the viewport, since a modal sheet and its backdrop are in the top layer. The drag handle is a `<tanrei-handle>` in the shadow root, its `container` and `line` exported as the parts `handle` and `grip`; the sheet sets the Handle's custom properties to its own tokens on it (BSH-12), answers its `activate`, and keeps it `inert` while the sheet has one height (BSH-11).	A view modifier on the view the sheet covers, as `.sheet` is: `.tanreiBottomSheet(isPresented: Binding<Bool>, variant:, detent: Binding<TanreiBottomSheetDetent>, dismissible:, handle:, handleLabel:, inset:, label:, onClose: ((TanreiSheetCloseReason) -> Void)?, content:)`. Closing writes false to `isPresented` and then calls `onClose` with the reason; a height the person chose is written to `detent` (detentChange). Modal: on iOS presented with `.fullScreenCover`, a clear presentation background and the system transition off, as `tanreiDialog` is (that presentation hides the rest of the app from VoiceOver); Tanrei draws the scrim, the sheet and the drag with a `DragGesture` (fling from its `velocity`, 0.5 pt/ms). Not the native `.sheet`: its dim cannot take the scrim token, and on iPad in a regular width it becomes a centred form, not a bottom sheet. macOS, which has no full-screen cover, draws the modal sheet as an overlay of the modified view with the modal trait. Standard: `.overlay(alignment: .bottom)` of the modified view. Initial focus is `.defaultFocus` or an `@AccessibilityFocusState` the product passes; Escape is `.onKeyPress(.escape)` and the escape gesture `.accessibilityAction(.escape)`. Snapshot harness: renders `TanreiBottomSheetSurface` (the sheet and, for a modal sheet, the scrim) in place in a 400 × 720 frame over a `surface` page, because a snapshot of the presenting view does not include a presented window. Not built on this platform yet: the header — headline, closable, closeLabel and dividerVisibility, the close reason close (BSH-28, BSH-29) — and the report of a sheet with no way out a person can see (BSH-30).	`TanreiBottomSheet(visible, onClose: (TanreiSheetCloseReason) -> Unit, variant, detent, onDetentChange, dismissible, handle, handleLabel, inset, contentDescription, initialFocus: FocusRequester?, content)`. `visible` rather than calling it only while open, so that the exit motion can run before the sheet goes; the caller sets `visible` to false from `onClose`. The sheet keeps a height the person chose until `detent` changes (BSH-21). Modal: drawn in a `Dialog` window of its own, as `TanreiDialog` and the modal drawer are, with `usePlatformDefaultWidth = false`, `decorFitsSystemWindows = false` and the window's own dim off (Tanrei draws the scrim); the window traps focus, answers back and hides the content behind from TalkBack; the sheet sets a pane title from `contentDescription`. Standard: fills its parent (a `Box` over the content) and draws the sheet at its bottom edge; the part above takes no touches. Drag with `Modifier.draggable` and nested scroll for BSH-10; fling and slop from `ViewConfiguration`. Snapshot harness: renders `TanreiBottomSheetContent` (the sheet and, for a modal sheet, the scrim) in place in a 400 × 720 dp box over a `surface` page; the window itself is covered by instrumented tests. Not built on this platform yet: the header — headline, closable, closeLabel and dividerVisibility, the close reason close (BSH-28, BSH-29) — and the report of a sheet with no way out a person can see (BSH-30).	`TanreiBottomSheet(variant:, open:, onClose: ValueChanged<TanreiSheetCloseReason>, detent:, onDetentChanged:, dismissible:, showHandle:, handleSemanticLabel:, inset:, semanticLabel:, child:)`, controlled: the caller sets `open` to false from `onClose`. The product places it in a `Stack` over what it covers — for a modal sheet, a `Stack` over the whole page, as the modal navigation drawer — not `showModalBottomSheet`, which needs Material. The modal form draws its scrim over the whole `Stack`, keeps focus in a `FocusScope`, blocks the page's semantics (`BlockSemantics`), names itself with `Semantics(scopesRoute: true, namesRoute: true)`, answers back through `PopScope` and Escape through `Shortcuts`/`Actions`. Initial focus is `autofocus: true` on a focusable widget. Drag with a vertical drag recogniser; fling `kMinFlingVelocity`, slop `kTouchSlop`. Snapshot harness: a golden of the whole 400 × 720 surface with the sheet in a `Stack` over a `surface` page. Not built on this platform yet: the header — headline, closable, closeLabel and dividerVisibility, the close reason close (BSH-28, BSH-29) — and the report of a sheet with no way out a person can see (BSH-30).	Controlled: `open`, `onClose(reason)`, `detent`, `onDetentChange`; the caller sets `open` to false from `onClose`. Modal: presented in a transparent `Modal` with `animationType="none"`, `statusBarTranslucent` and `navigationBarTranslucent` (Tanrei draws the scrim and the motion); `onRequestClose` (Android back, and Escape on a hardware keyboard) is close with the reason `back` or `escape`. Standard: a `View` positioned absolutely at the bottom of its parent. Drags with `PanResponder` (no gesture-handler dependency): slop 8 pt, fling 0.5 pt/ms. The on-screen keyboard is read from `Keyboard` events. Initial focus is an `initialFocusRef` the product passes, moved with `AccessibilityInfo.setAccessibilityFocus`. Insets come from the sheet's own `insets` prop, falling back to `TanreiProvider`'s `insets`; the package takes no safe-area dependency. Snapshot harness: renders `BottomSheetSurface` (the sheet and, for a modal sheet, the scrim) in place in a 400 × 720 view over a `surface` page, since a `Modal` is a native window the snapshot does not include. React Native cannot hand one gesture from the sheet to the content's native scroll view partway through, so BSH-10's hand-off takes two gestures there; the package takes no gesture-handler dependency (as it takes no safe-area one). Not built on this platform yet: the header — headline, closable, closeLabel and dividerVisibility, the close reason close (BSH-28, BSH-29) — and the report of a sheet with no way out a person can see (BSH-30).

Tokens

Token	Aliases	Resolved (light)
`--tanrei-comp-bottom-sheet-close-button-variant`	—	1
`--tanrei-comp-bottom-sheet-container-color`	`sys.color.surface-container-low`	#f9f9f9
`--tanrei-comp-bottom-sheet-container-elevation`	`sys.elevation.level2`	0px 0px 0px 1px rgb(0 0 0 / 0.08), 0px 1px 2px 0px rgb(0 0 0 / 0.04)
`--tanrei-comp-bottom-sheet-container-margin-block-start`	`sys.space.space600`	48px
`--tanrei-comp-bottom-sheet-container-max-width`	—	640px
`--tanrei-comp-bottom-sheet-container-padding`	`sys.space.space200`	16px
`--tanrei-comp-bottom-sheet-container-partial-fraction`	—	0.5
`--tanrei-comp-bottom-sheet-container-shape`	`sys.shape.corner.large`	12px
`--tanrei-comp-bottom-sheet-content-color`	`sys.color.on-surface`	#1b1b1b
`--tanrei-comp-bottom-sheet-divider-color`	`sys.color.outline-variant`	#000000 · 8%
`--tanrei-comp-bottom-sheet-divider-visibility`	`sys.behavior.divider-visibility`	0
`--tanrei-comp-bottom-sheet-divider-width`	`sys.border.hairline`	1px
`--tanrei-comp-bottom-sheet-drag-handle-container-color`	`comp.handle.standard.container.color`	#000000 · 0%
`--tanrei-comp-bottom-sheet-drag-handle-focused-container-color`	—	#848484 · 10%
`--tanrei-comp-bottom-sheet-drag-handle-focused-grip-color`	—	#848484
`--tanrei-comp-bottom-sheet-drag-handle-focused-state-layer-color`	—	#848484
`--tanrei-comp-bottom-sheet-drag-handle-grip-color`	`comp.handle.standard.line.color`	#848484
`--tanrei-comp-bottom-sheet-drag-handle-hovered-container-color`	—	#848484 · 8%
`--tanrei-comp-bottom-sheet-drag-handle-hovered-grip-color`	—	#4b4b4b
`--tanrei-comp-bottom-sheet-drag-handle-hovered-state-layer-color`	—	#848484
`--tanrei-comp-bottom-sheet-drag-handle-pressed-container-color`	—	#848484 · 10%
`--tanrei-comp-bottom-sheet-drag-handle-pressed-grip-color`	—	#4b4b4b
`--tanrei-comp-bottom-sheet-drag-handle-pressed-state-layer-color`	—	#848484
`--tanrei-comp-bottom-sheet-drag-handle-state-layer-color`	`comp.bottom-sheet.drag-handle.grip.color`	#848484
`--tanrei-comp-bottom-sheet-focused-opacity`	—	1
`--tanrei-comp-bottom-sheet-handle-container-height`	`comp.handle.container.breadth.medium`	24px
`--tanrei-comp-bottom-sheet-handle-container-shape`	`comp.handle.container.shape`	9999px
`--tanrei-comp-bottom-sheet-handle-container-width`	`comp.handle.container.length.medium`	48px
`--tanrei-comp-bottom-sheet-handle-grip-height`	`comp.handle.line.thickness.medium`	4px
`--tanrei-comp-bottom-sheet-handle-grip-width`	`comp.handle.line.length.medium`	32px
`--tanrei-comp-bottom-sheet-handle-margin-block`	`sys.space.space150`	12px
`--tanrei-comp-bottom-sheet-header-gap`	`sys.space.space100`	8px
`--tanrei-comp-bottom-sheet-header-height`	—	64px
`--tanrei-comp-bottom-sheet-header-padding-inline-end`	`sys.space.space150`	12px
`--tanrei-comp-bottom-sheet-headline-color`	`sys.color.on-surface`	#1b1b1b
`--tanrei-comp-bottom-sheet-hovered-opacity`	—	1
`--tanrei-comp-bottom-sheet-motion-enter-duration`	`sys.motion.role.appear.sheet.enter`	400ms
`--tanrei-comp-bottom-sheet-motion-enter-easing`	`sys.motion.easing.enter`	cubic-bezier(0.2, 0, 0, 1)
`--tanrei-comp-bottom-sheet-motion-exit-duration`	`sys.motion.role.appear.sheet.exit`	350ms
`--tanrei-comp-bottom-sheet-motion-exit-easing`	`sys.motion.easing.exit`	cubic-bezier(0.3, 0, 1, 1)
`--tanrei-comp-bottom-sheet-motion-feedback-duration`	`comp.handle.motion.feedback-duration`	450ms
`--tanrei-comp-bottom-sheet-motion-state-duration`	`comp.handle.motion.state-duration`	200ms
`--tanrei-comp-bottom-sheet-motion-state-easing`	`comp.handle.motion.state-easing`	cubic-bezier(0.2, 0, 0, 1)
`--tanrei-comp-bottom-sheet-pressed-opacity`	—	1
`--tanrei-comp-bottom-sheet-scrim-blur`	`comp.modal-layer.scrim.blur`	0px
`--tanrei-comp-bottom-sheet-scrim-color`	`comp.modal-layer.scrim.color`	#000000 · 40%
`--tanrei-comp-bottom-sheet-headline-typescale`	`sys.typescale.heading-5`	500 16px/1.5

Fixtures

Canonical renderings. Every platform snapshots each fixture under the same id so the results can be compared.

modal

open: true handleLabel: Resize sheet label: Save photo Drawn alone in a window of 400 × 720

modal-partial

open: true detent: partial handleLabel: Resize sheet label: Terms of service Drawn alone in a window of 400 × 720

modal-full

open: true detent: full handleLabel: Resize sheet label: Terms of service Drawn alone in a window of 400 × 720

no-handle

open: true handle: false label: Save photo Drawn alone in a window of 400 × 720

standard

variant: standard open: true handleLabel: Resize sheet label: Nearby places Drawn alone in a window of 400 × 720

modal-header

open: true handleLabel: Resize sheet headline: Save photo closable: true closeLabel: Close Drawn alone in a window of 400 × 720

no-handle-header

open: true handle: false headline: Save photo closable: true closeLabel: Close Drawn alone in a window of 400 × 720

standard-header

variant: standard open: true handleLabel: Resize sheet label: Cafés and bakeries nearby headline: Nearby places closable: true closeLabel: Close nearby places Drawn alone in a window of 400 × 720

Generated from specs/bottom-sheet.spec.json, tokens/comp/bottom-sheet.tokens.json, design/tokens/

Guidelines

When to use

Use a bottom sheet on a compact screen, where there is no room beside the content, for something that belongs to the screen but is not its main subject: the places near a point on a map, the ways to share a photo, a short choice or form. The sheet rises from the edge the thumb is closest to.

Use a side sheet for the same kind of content on a wide window, where it can sit beside the content instead of over it. Use a dialog for a decision the task cannot go on without. Use a navigation drawer for a product’s destinations, not a bottom sheet.

Several actions from the main action. When a screen’s main action comes in a few related forms (a new document, a folder or an upload), the main action button opens a modal bottom sheet that lists them. In the Tanrei system this takes the place of the FAB menu, which it does not ship.

Several actions from the main action: open the sheet with the button

add

Document

Folder

Upload a file

Form	What it is	Use for
Modal (default)	A modal overlay. The sheet slides up over a scrim that dims the whole window. Everything outside it is inert, and focus stays inside until it closes.	A step the person finishes or dismisses before going back: sharing, a choice, a short form.
Standard	A layout region. The sheet covers the bottom of its parent with no scrim, and the content above it stays usable. Tab moves between the sheet and the content, and focus leaving the sheet never closes it.	Content the person uses together with the screen, such as a list of places over a map.

Both forms read the same tokens: only the scrim and the behaviour set them apart, so a design system does not give them different looks.

The layout regions are a standard navigation drawer (its collapsed form included), an app bar and a standard side sheet, which all sit beside or above the content. A standard bottom sheet covers part of its parent instead, but it is a layout region too, because what matters is the behaviour: it is not modal, it draws no scrim, and the content stays usable while it is open. A sheet that closed whenever focus left it could not be used from the keyboard alongside the map it describes.

The standard sheet does not move or pad what it covers. If the end of your scrolling content must stay visible above the sheet, pad that content by the sheet’s partial height.

Heights

detent has two values. At partial the sheet takes a share of the area it covers, half with the default tokens. At full it reaches up to a small margin below the area’s top. The area is the window below its top inset for a modal sheet, and the parent for a standard one. While the on-screen keyboard is shown, the area ends at the keyboard, so the sheet sits on it.

The sheet is only as tall as its content. A sheet whose content fits within the partial height has one height, and detent changes nothing. While the content is taller, the sheet has two heights, and the person moves between them by dragging or with the drag handle. Each such move emits detentChange with the new height. On the web, Compose, Flutter and React Native, the sheet keeps the height the person chose until you set detent again. On SwiftUI it writes the height to the detent binding. Setting detent yourself moves the sheet without emitting anything.

The drag handle and gestures

The drag handle is the short bar at the top of the sheet, in a row that stays in place while the content scrolls. With handle on, it is drawn on every sheet.

A control, when there is somewhere to go. While the sheet has two heights, the handle is a button named by handleLabel, with the expanded state at full height. A press, Enter or Space moves the sheet to its other height. While the sheet has one height, the handle is drawn at rest as a sign that the sheet can be dragged, but it cannot be focused or pressed and assistive technology does not see it.
Its target. The whole row across the handle is its hit area, at least the minimum target in each direction, although the bar itself is small.
Dragging. The person can drag the sheet up and down by the handle’s row, by the padding around the content, or by the content itself. The sheet follows once the finger or pointer has moved past the platform’s touch slop (8 points where the platform names none), and never rises above its full height.
Letting go. On release, a fling settles the sheet at the next height in its direction, and a slower release at the nearest height. A fling is a release faster than the platform’s minimum fling velocity, or 0.5 points per millisecond where the platform names none.
Dragging to close. A release below half of the lowest height, or a downward fling from the lowest height, asks the sheet to close with the reason drag, while dismissible is true. The sheet holds where the drag left it for one frame, then slides out if you set open to false, or settles back if you did not. While dismissible is false it settles at its lowest height.
Content that scrolls. An upward drag on the content first raises the sheet to full height, then scrolls the content. A downward drag first scrolls the content back to its top, then lowers the sheet. Where a platform cannot pass one gesture from the sheet to the content’s scroll, the second part takes a second drag (see the known platform gaps below). The keyboard and assistive technology can scroll the content at either height.

Dragging is never the only way. The handle changes the height with one press or from the keyboard, and a modal sheet also closes with the scrim, Escape or back. A standard sheet, and a modal one whose dismissible is false, has no such second way to close, so give it a button that closes it.

Opening, focus and closing

Opening. The sheet slides up from below the bottom edge. A modal sheet fades in its scrim over the whole window at the same time. A sheet shown with open already true appears in place, without motion. A standard one then leaves focus where it is. A modal one moves focus in as if it had just opened, because nothing behind it can take focus any more.
Focus in. Opening moves focus to the element you marked, or to the sheet itself, in both forms. Focus moves when the sheet opens, not when its motion ends.
Focus kept in, modal only. In a modal sheet, Tab from the last focusable element goes to the first, and Shift+Tab from the first goes to the last. Screen-reader navigation stays inside, and the content behind does not scroll. A standard sheet keeps nothing: Tab moves on to the content, and the sheet stays open.
Closing. When the sheet closes while focus is inside it, focus returns to the element that had it when the sheet opened.
Stacking. A dialog, a menu or another modal sheet opened from a modal sheet stacks above it. Escape dismisses only the topmost, and the sheet gets back the focus that overlay returns.
Motion. Where motion is reduced, the sheet fades in and out in place without sliding. On Android, whose setting removes every animation, it appears and disappears at once.

Do

Put the sheet’s task in plain view: a title at the top of the content, and a Done or Close button when the sheet has no other way to close.
Turn inset off for a list whose rows carry their own padding, so that the rows reach the edges.
Leave the handle on for any sheet whose content can grow taller than its partial height, so that keyboard and switch users can change its height.
Use the standard form when the person needs the content above the sheet while it is open.

Don’t

Don’t set dismissible to false unless the person must finish the sheet’s task with one of its own controls.
Don’t use a modal sheet for a decision that must interrupt the person. Use a dialog.
Don’t put a product’s navigation in a bottom sheet. Use a navigation drawer or a navigation bar.
Don’t stack sheet on sheet for a task with steps. Change the content of one sheet instead.

Accessibility

Role: dialog
Labeling: The sheet is named by label, or by its headline where label is empty: a modal dialog while variant is modal, a region while it is standard. The headline is a heading; the close button is named by closeLabel; the divider is decorative. The drag handle, while the sheet has two heights, is a button named by handleLabel with the expanded state (true at full height); at one height it is hidden. The grip is decorative.
Minimum target: The hit area meets the minimum target size even when the visual size is smaller. minimum 32px · pointer 44px · spacing 8px · touch 48px

Keyboard

Keys	Action
`Tab / Shift+Tab`	Moves focus through the drag handle (while it is interactive), the close button (while closable is true) and the content's focusable elements, in that order. In an open modal sheet it wraps and never leaves the sheet; from a standard sheet it moves on to the content, and the sheet stays open.
`Enter` / `Space`	On the drag handle, moves the sheet to its other height (partial or full). On the close button, asks the sheet to close (close, reason close).
`Escape`	Asks an open modal sheet to close (close, reason escape) while dismissible is true; with stacked overlays, only the topmost. A standard sheet ignores it.

Notes

Dragging is never the only way (WCAG 2.5.7): the drag handle changes the height with a single press or from the keyboard, and a modal sheet closes with Escape, back or a press on the scrim. A standard sheet, and a modal one whose dismissible is false, closes only by a drag, its close button or the product: set closable, or put a Close or Done button in its content.
The standard form is a layout region, although it covers the bottom of the content rather than pushing it aside: the person works in the content and in the sheet at once, so focus leaving it never closes it. The modal form is a modal overlay.
Web: the modal form is a native <dialog> opened with showModal() inside the shadow root, so the rest of the page is inert and the sheet is in the top layer; ::backdrop draws the scrim. Its cancel event (Escape) is cancelled and becomes close with the reason escape; the product then sets open to false. The standard form is a region (a <section> named by label) positioned at the bottom of its containing block. The `autofocus` attribute on a slotted element marks initial focus.
Where a platform presents the modal sheet in a window of its own (Compose's Dialog, React Native's Modal), the window's own dim and transition are switched off and Tanrei draws the scrim and the motion, so every platform draws the same color.
The sheet does not move or pad the content a standard sheet covers; a product whose content must stay visible above the sheet pads its scrolling content by the sheet's partial height.
How a state looks is a value decision of the active design system; components read the state's tokens and never compute the effect themselves.

Generated from specs/bottom-sheet.spec.json, tokens/sys/measure.tokens.json

What the component handles

A modal sheet is exposed as a modal dialog named by label, or by its headline where label is empty. A standard sheet is a region named the same way, a landmark on the web.
The headline is a heading. The close button is a Tanrei icon-only Button named by closeLabel, with the Button’s own minimum target, focus ring and states; it asks the sheet to close with the reason close in either form, whatever dismissible says. The divider below the header is decorative.
While a modal sheet is open, everything outside it is inert and hidden from assistive technology, and focus and screen-reader navigation stay inside it. A standard sheet makes nothing inert.
Opening moves focus to the element you marked, or to the sheet. Closing returns focus to the element that had it when the sheet opened. This holds for both forms.
Escape, the platform’s back and a press on the scrim ask a modal sheet to close, while dismissible is true. A standard sheet ignores Escape and back.
The drag handle is a handle, always drawn, given the sheet’s own tokens. While the sheet has two heights it is one focusable button named by handleLabel, expanded at full height. Enter and Space move the sheet to its other height. At one height the handle is hidden from assistive technology. The grip is always hidden.
The handle’s hit area is at least the minimum target, and its focus ring shows for keyboard focus only.
The content scrolls inside the sheet, and keyboard focus and assistive technology can scroll it at either height.
Larger text makes the sheet grow with its content, up to the height its detent allows, and the content scrolls beyond that. The handle does not scale.
The sheet’s color reaches under the bottom system inset, and its content stays above that inset and above the on-screen keyboard.
Debug builds report a sheet with neither a label nor a headline, an interactive handle without a handleLabel, a close button without a closeLabel, a sheet with no handle and no close button that can still be dismissed (nothing on screen says how), and an unknown variant, detent or dividerVisibility.

Known platform gaps:

A mouse drag on the content moves the sheet as a touch does, so text in a sheet cannot be selected by dragging down it while the sheet can still move.
SwiftUI, Compose, Flutter and React Native do not draw the header yet: headline, closable, closeLabel and dividerVisibility, and the reason close, are on the web only for now.
Web: on touch, the browser decides who takes a gesture when it begins, so the hand-off between the sheet and the content’s scroll takes a second gesture. A mouse or a pen hands off within one drag. Touch dragging is not yet covered by a test. In Firefox the sheet leaves at once instead of sliding out, as the dialog does.
SwiftUI has neither a dialog nor a region role: the sheet is a container named by label, with the modal trait while modal. The handle has no expanded state, so its value says “expanded” or “collapsed”, in English only. SwiftUI cannot move focus to the sheet itself when nothing is marked, and gives keyboard focus back to nothing when it closes; on iOS the modal cover gives VoiceOver back. On macOS a modal sheet covers only the view the modifier is attached to, so attach it to the window’s root.
SwiftUI on iOS: below its full height, a drag on the content raises the sheet and the next drag scrolls, and the content does not scroll there, not even for VoiceOver or the keyboard. Plain text in the content takes the body font without its line height, so two lines are 40 points tall where the other platforms draw 44.
SwiftUI: the bottom inset and the on-screen keyboard, the hardware keyboard, Escape and the iOS escape gesture have not been run on a device or tested by pressing them.
Compose: the sheet scrolls its content itself, so give it a plain column, not a lazy list. While a modal sheet closes, its window keeps focus until the exit motion ends. Its drags are verified under Robolectric only, not on a device.
Flutter: a standard sheet is a named container, not a region landmark, because Flutter 3.32 has no such role. The sheet has not yet been checked with TalkBack and VoiceOver on a device.
React Native cannot tell which element had focus, so when the sheet closes, focus goes where the platform puts it, not back to the element that opened it, as with the dialog and the navigation drawer. Without initialFocusRef, opening moves only the screen reader, to the sheet.
React Native cannot hand one gesture from the sheet to the content’s scroll midway, so the rest of that drag is lost and the next one scrolls. The Modal, the drag, the keyboard avoidance and the insets are verified in Jest only, never on a device.
Under cupertino, the grip is drawn in Apple’s light outline color and measures 1.8:1 against the sheet in the light scheme and 2.2:1 in the dark one, below the 3:1 a control’s boundary needs. The medium and high contrast schemes bring it to 4.5:1 or more. The two figures that fall short are measurements kept as information: Tanrei’s accessibility criteria do not apply to an imitation preset.
Under m3-like, the sheet at full height keeps the default system’s top margin: Material’s value waits for the fidelity reference to cover the bottom sheet.

What you need to do

Give every sheet a label or a headline, such as “Save photo”. It names the dialog or the region.
Give the handle a handleLabel, such as “Resize sheet”, in your product’s language.
Close the sheet yourself: set open to false in answer to close (the close event on the web, onClose on Compose, Flutter and React Native), and from your own Done or Close button. On SwiftUI the sheet writes false to the binding for you.
Give a standard sheet, and a modal sheet whose dismissible is false, a visible button that closes it: its close button (closable, with a closeLabel) or one of your own. Dragging must not be the only way out.
Mark initial focus where it helps, such as the first field of a short form.
On React Native, pass initialFocusRef, move focus back to the sheet’s opener yourself after it closes, and pass the window’s insets to the sheet’s insets or to TanreiProvider.

Source code and issues on GitHub