diff --git a/CLAUDE.md b/CLAUDE.md
index 4c81e950..04dd6d61 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -30,9 +30,10 @@ The modernization roadmap (React 17/18 upgrade, `semantic-ui-react` exit, projec
 - `npm run test:pack` — `build-lib`, then the packaging budgets (`test:pack:budget`, `scripts/check-package-budget.js`) and a server-render smoke of the packed tarball (`test:pack:consumer`). `npm run test:pack:peers` repeats the smoke on React 16.14, 17.0.2 and 19.3.0, from the same fixtures as the jest legs. `npm run test:pack:browser` (after `build-lib`) loads the packed tarball in Chromium: a throwaway host (`scripts/packed-workspace.js`, shared with the server smoke) bundles it with its own React beside the published `static/all.css`, and `e2e/packed/tarball.packed.js` (`playwright.packed.config.js`) checks that it renders, responds and styles only its own wrapper; CI runs it in the `browser` job. `npm run test:pack:browser:peers` runs the same page on React 16.14, 17 and 19 from the jest legs' fixtures, mounting through `ReactDOM.render` on 16 and 17 as 0.34.x hosts do; CI runs it there too
 - `npm run test:perf` (after `build-lib`) — what the packed tarball's documents cost in Chromium.
   - **What it measures:** the main thread's busy time (the DevTools protocol's `TaskDuration`) for a mount, and the
-    median of five runs of each action (an edit, a blur, a pick, a tab switch), in five documents of
-    `scripts/fixtures/packed-perf-entry.js`. The documents include a 200-row period table, a 200-row table with a
-    Select column, and two tabs whose second holds a 200-row table.
+    median of five runs of each action (an edit, a blur, a pick, a tab switch, a table shown and taken away), in eight
+    documents of `scripts/fixtures/packed-perf-entry.js`. The documents include a 200-row period table, a 200-row
+    table with a Select column, two tabs whose second holds a 200-row table, and that table beside 200 required
+    fields, shown by a `showIf`, in a popup, or in an Expand.
   - **Where it runs:** in the same throwaway host as `test:pack:browser`, under `playwright.perf.config.js`, with
     `e2e/perf/scenarios.perf.js`. It prints the medians and writes them to `test-results-perf/perf-results.json`.
   - **Comparing versions:** `--tarball=<file>` measures a tarball packed elsewhere, such as another commit's, so two
diff --git a/e2e/perf/scenarios.perf.js b/e2e/perf/scenarios.perf.js
index 8b9e4ec6..8c1b3d87 100644
--- a/e2e/perf/scenarios.perf.js
+++ b/e2e/perf/scenarios.perf.js
@@ -7,8 +7,9 @@
  * thread's busy time, the DevTools protocol's `TaskDuration`, over the mount and over each action, an action being
  * what a user does and everything it sets off until the page is idle again (the 300 ms typing debounce included).
  * Each action runs five times, and the median is what counts. After its runs, an edit or a pick checks that its field
- * shows the last run's value, so that an action that stops changing anything fails instead of measuring nothing. A tab
- * switch waits for the table's field to be there, and a switch back for it to be gone. Each test writes its
+ * shows the last run's value, so that an action that stops changing anything fails instead of measuring nothing. An
+ * action that brings a table, a tab switch or a `showIf`, a popup or an Expand, waits for the table's field to be there,
+ * and the one that takes it away for it to be gone: a collapse, when its animation ends. Each test writes its
  * document's numbers to PERF_OUT before it checks them, so that a document over its ceilings still reports, and so do
  * the ones after it. scripts/test-packed-perf.js runs it (`npm run test:perf`) and prints them; CI runs it in the
  * advisory `browser-perf` job, which reports and never blocks.
@@ -37,6 +38,9 @@ const CEILINGS = {
     selectForm: { mount: 340, pick: 100, edit: 100 },
     numberTable: { mount: 780, edit: 100 },
     tabs: { mount: 210, switch: 360, back: 100 },
+    reveal: { mount: 270, show: 270, hide: 100 },
+    popup: { mount: 260, open: 340, close: 110 },
+    expand: { mount: 280, expand: 600, collapse: 400 },
 }
 
 const median = values => [...values].sort((a, b) => a - b)[Math.floor(values.length / 2)]
@@ -73,6 +77,21 @@ async function record (scenario, name, measure, action) {
     results[scenario][name] = { median: median(runs), runs }
 }
 
+/**
+ * Runs `there` and then `back`, REPEAT times, and records the median of what each cost: an action that brings a
+ * table, and the one that takes it away again.
+ */
+async function alternate (scenario, [thereName, backName], measure, there, back) {
+    const theres = []
+    const backs = []
+    for (let i = 0; i < REPEAT; i++) {
+        theres.push(await measure(there))
+        backs.push(await measure(back))
+    }
+    results[scenario][thereName] = { median: median(theres), runs: theres }
+    results[scenario][backName] = { median: median(backs), runs: backs }
+}
+
 /**
  * Adds a scenario's numbers to PERF_OUT, then checks them against its ceilings. A failed test's worker is replaced,
  * and this module's state with it, so the file, not `results`, is what holds every scenario's.
@@ -147,25 +166,64 @@ test('two tabs, the second a 200-row table: a switch to it, and back', async ({
     const summary = page.getByRole('tab', { name: 'Summary', exact: true })
     const cell = page.locator('input[name="rows[1].note"]')
     // A switch waits for the table's field to be there, and a switch back for it to be gone.
-    const switches = []
-    const backs = []
-    for (let i = 0; i < REPEAT; i++) {
-        switches.push(await measure(async () => {
-            await rows.click()
-            await cell.waitFor()
-        }))
-        backs.push(await measure(async () => {
-            await summary.click()
-            await cell.waitFor({ state: 'detached' })
-        }))
-    }
-    results.tabs.switch = { median: median(switches), runs: switches }
-    results.tabs.back = { median: median(backs), runs: backs }
+    await alternate('tabs', ['switch', 'back'], measure, async () => {
+        await rows.click()
+        await cell.waitFor()
+    }, async () => {
+        await summary.click()
+        await cell.waitFor({ state: 'detached' })
+    })
     await rows.click()
     await expect(cell).toHaveValue('note 1')
     check('tabs')
 })
 
+test('a `showIf` that shows a 200-row table beside 200 required fields, and hides it', async ({ page }) => {
+    const { mount, measure } = await open(page, 'reveal')
+    results.reveal = { mount: { median: mount, runs: [mount] } }
+    const show = page.getByRole('textbox', { name: 'Show', exact: true })
+    const cell = page.locator('input[name="rows[1].note"]')
+    await alternate('reveal', ['show', 'hide'], measure, async () => {
+        await show.fill('yes')
+        await cell.waitFor()
+    }, async () => {
+        await show.fill('no')
+        await cell.waitFor({ state: 'detached' })
+    })
+    check('reveal')
+})
+
+test('a popup that holds a 200-row table beside 200 required fields: opening it, and closing it', async ({ page }) => {
+    const { mount, measure } = await open(page, 'popup')
+    results.popup = { mount: { median: mount, runs: [mount] } }
+    const opener = page.getByRole('button', { name: 'Open rows', exact: true })
+    const cell = page.locator('input[name="rows[1].note"]')
+    await alternate('popup', ['open', 'close'], measure, async () => {
+        await opener.click()
+        await cell.waitFor()
+    }, async () => {
+        await page.getByRole('dialog').press('Escape')
+        await cell.waitFor({ state: 'detached' })
+    })
+    check('popup')
+})
+
+test('an Expand that holds a 200-row table beside 200 required fields: expanding it, and collapsing it', async ({ page }) => {
+    const { mount, measure } = await open(page, 'expand')
+    results.expand = { mount: { median: mount, runs: [mount] } }
+    const title = page.getByRole('button', { name: 'Rows', exact: true })
+    const cell = page.locator('input[name="rows[1].note"]')
+    // A collapse waits for the content to go, when the animation ends.
+    await alternate('expand', ['expand', 'collapse'], measure, async () => {
+        await title.click()
+        await cell.waitFor()
+    }, async () => {
+        await title.click()
+        await cell.waitFor({ state: 'detached' })
+    })
+    check('expand')
+})
+
 test('a 200-row table of bounded number fields: an edit of a number', async ({ page }) => {
     const { mount, measure } = await open(page, 'numberTable')
     results.numberTable = { mount: { median: mount, runs: [mount] } }
diff --git a/scripts/fixtures/packed-perf-entry.js b/scripts/fixtures/packed-perf-entry.js
index 9a99d047..79de09bf 100644
--- a/scripts/fixtures/packed-perf-entry.js
+++ b/scripts/fixtures/packed-perf-entry.js
@@ -10,6 +10,19 @@ const ROWS = 200
 const range = count => Array.from({ length: count }, (_, i) => i)
 const records = [{ id: 'a', name: 'A' }, { id: 'b', name: 'B' }, { id: 'c', name: 'C' }]
 const choices = [{ text: 'A', value: 'a' }, { text: 'B', value: 'b' }, { text: 'C', value: 'c' }]
+// A 200-row table of a required text column and a bounded number column, and its rows.
+const rowsTable = {
+    view: 'Table',
+    name: 'rows',
+    headers: [
+        { id: 'note', label: 'Note', renderCell: { view: 'Input', name: 'note', validate: 'required' } },
+        { id: 'qty', label: 'Qty', renderCell: { view: 'Input', type: 'number', name: 'qty', min: 0, max: 100000 } },
+    ],
+}
+const tableRows = () => ({ rows: range(ROWS).map(i => ({ note: `note ${i}`, qty: i })) })
+// 200 required fields beside it, which every field that comes or goes used to validate, each.
+const besideFields = range(ROWS).map(i => ({ view: 'Input', name: `field${i}`, label: `Field ${i}`, validate: 'required' }))
+const besideValues = () => Object.fromEntries(range(ROWS).map(i => [`field${i}`, `value ${i}`]))
 const periodField = name => ({
     view: 'Input',
     name,
@@ -57,27 +70,41 @@ const SCENARIOS = {
         },
         data: { other: 'text', ...Object.fromEntries(range(100).map(i => [`choice${i}`, 'a'])) },
     }),
-    // Two tabs, the second a 200-row table of a required text column and a bounded number column, which mounts and
-    // unmounts with its tab.
+    // Two tabs, the second the 200-row table, which mounts and unmounts with its tab.
     tabs: () => ({
         meta: {
             view: 'Tabs',
             items: [
                 { tab: 'Summary', content: { view: 'Text', children: 'Nothing to edit here' } },
-                {
-                    tab: 'Rows',
-                    content: {
-                        view: 'Table',
-                        name: 'rows',
-                        headers: [
-                            { id: 'note', label: 'Note', renderCell: { view: 'Input', name: 'note', validate: 'required' } },
-                            { id: 'qty', label: 'Qty', renderCell: { view: 'Input', type: 'number', name: 'qty', min: 0, max: 100000 } },
-                        ],
-                    },
-                },
+                { tab: 'Rows', content: rowsTable },
+            ],
+        },
+        data: tableRows(),
+    }),
+    // The 200-row table, which a `showIf` shows and hides, beside 200 required fields.
+    reveal: () => ({
+        meta: {
+            view: 'Col',
+            items: [{ view: 'Input', name: 'show', label: 'Show' }, ...besideFields, { ...rowsTable, showIf: { name: 'show', equal: 'yes' } }],
+        },
+        data: { show: 'no', ...besideValues(), ...tableRows() },
+    }),
+    // A popup that holds the 200-row table, beside 200 required fields.
+    popup: () => ({
+        meta: {
+            view: 'Col',
+            items: [
+                { view: 'Button', children: 'Open rows', onClick: { name: 'popupOpen', args: ['rows'] } },
+                ...besideFields,
+                { view: 'Popup', id: 'rows', title: 'Rows', items: [rowsTable] },
             ],
         },
-        data: { rows: range(ROWS).map(i => ({ note: `note ${i}`, qty: i })) },
+        data: { ...besideValues(), ...tableRows() },
+    }),
+    // An Expand that holds the 200-row table, beside 200 required fields. Its content goes when its animation ends.
+    expand: () => ({
+        meta: { view: 'Col', items: [...besideFields, { view: 'Expand', title: 'Rows', items: [rowsTable] }] },
+        data: { ...besideValues(), ...tableRows() },
     }),
     // A column of number fields with bounds, beside a text column.
     numberTable: () => ({