diff --git a/README.md b/README.md
index d4dc3bb..f77b0f6 100644
--- a/README.md
+++ b/README.md
@@ -651,8 +651,22 @@ Inspector unter **Objekt · Auswahl**: horizontale **Ausrichtung**
 **Prozent** 0/2 Stellen, **Datum**/**Zeit**/**Datum + Zeit** — kombiniert mit
 der Locale unten — sowie **Datum (ISO)**, das immer `JJJJ-MM-TT` zeigt,
 unabhängig von der Locale), **Zell-Textfarbe**,
-**Zell-Füllfarbe**, **Fett**/**Kursiv**, „Formatierung entfernen". Auch exakte
-**Spaltenbreite** und **Zeilenhöhe** der Fokuszelle.
+**Zell-Füllfarbe**, **Fett**/**Kursiv**/**Unterstrichen**, „Formatierung
+entfernen". Auch exakte **Spaltenbreite** und **Zeilenhöhe** der Fokuszelle.
+Per Tastatur: `Strg`/`Cmd`+`Umschalt`+`B` (oder `F`) fett, `+I` kursiv, `+U`
+unterstrichen; jeweils ein, wenn noch nicht jede Zelle der Auswahl es hat,
+sonst aus.
+
+### Hilfe (`?`, F1)
+
+Das `?` in der Symbolleiste, **Datei › Hilfe …** oder `F1` öffnet die
+eingebaute Hilfe ([`HelpModal.vue`](app/frontend/components/HelpModal.vue)):
+Themen für Benutzer, alle Tastenkürzel und die Formelfunktionen samt
+Rechenzeichen, mit einer Suche über alles. Themen und Kürzel stehen in
+[`data/help.ts`](app/frontend/data/help.ts) und werden von Hand gepflegt, wer
+ein Kürzel oder eine sichtbare Funktion ändert, passt sie dort mit an. Die
+Funktionsliste kommt aus `data/codeReference.ts` und ist damit immer
+vollständig.
 
 ### Einstellungen (⚙, links neben dem Titel)
 
diff --git a/app/frontend/components/AppToolbar.vue b/app/frontend/components/AppToolbar.vue
index 8fb473d..ab1e31c 100644
--- a/app/frontend/components/AppToolbar.vue
+++ b/app/frontend/components/AppToolbar.vue
@@ -4,6 +4,7 @@ import { useDocument } from '../store/document';
 import { useTheme } from '../composables/useTheme';
 import { useToasts } from '../composables/useToasts';
 import BaseModal from './BaseModal.vue';
+import HelpModal from './HelpModal.vue';
 import CustomFunctionsModal from './CustomFunctionsModal.vue';
 import NamedRangesModal from './NamedRangesModal.vue';
 import MacrosModal from './MacrosModal.vue';
@@ -120,6 +121,17 @@ const uploadOpen = ref(false);
 const loginOpen = ref(false);
 const loginReason = ref<string | undefined>();
 const accountMenuOpen = ref(false);
+const helpOpen = ref(false);
+
+// F1 opens the help from anywhere (also out of a cell editor -- the browser's
+// own F1 help is what preventDefault keeps away)
+function onHelpKey(e: KeyboardEvent) {
+  if (e.key !== 'F1') return;
+  e.preventDefault();
+  helpOpen.value = true;
+}
+onMounted(() => window.addEventListener('keydown', onHelpKey));
+onBeforeUnmount(() => window.removeEventListener('keydown', onHelpKey));
 
 function openLogin(reason?: string) {
   loginReason.value = reason;
@@ -470,10 +482,13 @@ async function onSample() {
         <li><button @click="runXlsxExport">Export · Arbeitsmappe (.xlsx)</button></li>
         <li><button @click="exportSelectedChartPng">Export · gewähltes Diagramm (.png)</button></li>
         <li class="sep" />
+        <li><button @click="helpOpen = true">Hilfe … (F1)</button></li>
         <li><button @click="aboutOpen = true">Über Numolus …</button></li>
       </ul>
     </div>
 
+    <button class="ibtn help" title="Hilfe (F1)" aria-label="Hilfe" @click="helpOpen = true">?</button>
+
     <button
       class="ibtn"
       :title="`Theme: ${themeLabel} (klicken zum Wechseln)`"
@@ -588,6 +603,7 @@ async function onSample() {
   />
   <LoginModal :open="loginOpen" :reason="loginReason" @close="loginOpen = false" />
   <UploadModal :open="uploadOpen" @close="uploadOpen = false" />
+  <HelpModal :open="helpOpen" @close="helpOpen = false" />
 
   <!-- Über / Impressum -->
   <BaseModal :open="aboutOpen" title="Über Numolus" @close="aboutOpen = false">
@@ -866,6 +882,11 @@ async function onSample() {
   cursor: pointer;
   transition: background-color 0.12s ease, color 0.12s ease;
 }
+/* the help button is a plain "?" rather than an icon */
+.ibtn.help {
+  font-size: 15px;
+  font-weight: 700;
+}
 .tgroup.accent .ibtn {
   color: var(--accent);
 }
diff --git a/app/frontend/components/FormulaBar.vue b/app/frontend/components/FormulaBar.vue
index db605f2..56798c2 100644
--- a/app/frontend/components/FormulaBar.vue
+++ b/app/frontend/components/FormulaBar.vue
@@ -1,7 +1,7 @@
 <script setup lang="ts">
 import { computed, nextTick, ref, watch } from 'vue';
 import { useDocument } from '../store/document';
-import { cycleReferenceLocks } from '../engine';
+import { cycleReferenceLocks, completeFormula } from '../engine';
 import { useFormulaAutocomplete } from '../composables/useFormulaAutocomplete';
 import { useKeyboardPointMode } from '../composables/useKeyboardPointMode';
 import { useToasts } from '../composables/useToasts';
@@ -113,6 +113,10 @@ function backToGrid() {
 
 function commit() {
   const sel = store.doc.selection;
+  // a forgotten closing ")" is completed rather than stored as an error; in
+  // the draft too, since the sync watch above skips changes made while the
+  // field still has focus (Enter commits before it blurs)
+  draft.value = completeFormula(draft.value);
   if (sel) store.setCellInput(sel.tableId, sel.anchor.col, sel.anchor.row, draft.value);
 }
 /** Lets the store insert a reference into this field when the user clicks a
diff --git a/app/frontend/components/HelpModal.vue b/app/frontend/components/HelpModal.vue
new file mode 100644
index 0000000..7d7cf30
--- /dev/null
+++ b/app/frontend/components/HelpModal.vue
@@ -0,0 +1,410 @@
+<script setup lang="ts">
+/**
+ * In-app help: topics and keyboard shortcuts from data/help.ts, plus the
+ * formula functions and operators from data/codeReference.ts (the same
+ * entries the macro/function editors' reference shows, so the list can't
+ * drift from the engine). One search box runs over all of it. Opened from
+ * the toolbar's "?" button, Datei › Hilfe or F1 (see AppToolbar.vue).
+ */
+import { computed, nextTick, ref, watch } from 'vue';
+import BaseModal from './BaseModal.vue';
+import { HELP_TOPICS, SHORTCUT_GROUPS, shortcutKeys, type KeyPlatform, type Shortcut } from '../data/help';
+import { matchesQuery, referenceFor } from '../data/codeReference';
+
+const props = defineProps<{ open: boolean }>();
+const emit = defineEmits<{ (e: 'close'): void }>();
+
+type Page = string; // a topic id, 'shortcuts' or 'functions'
+const page = ref<Page>(HELP_TOPICS[0].id);
+const query = ref('');
+const searchEl = ref<HTMLInputElement | null>(null);
+
+watch(
+  () => props.open,
+  (o) => {
+    if (!o) return;
+    query.value = '';
+    nextTick(() => searchEl.value?.focus());
+  },
+);
+
+const isMac = typeof navigator !== 'undefined' && /Mac|iPhone|iPad/.test(navigator.platform || navigator.userAgent);
+/** This device's platform: its column in the shortcut tables is highlighted,
+ *  and the topics' running text names its keys. */
+const platform: KeyPlatform = isMac ? 'mac' : 'pc';
+const keys = (k: string) => shortcutKeys(k, platform);
+/** Both columns are always shown -- the help is also read to explain the
+ *  app to someone on the other system. */
+const COLUMNS: { platform: KeyPlatform; label: string }[] = [
+  { platform: 'pc', label: 'Windows / Linux' },
+  { platform: 'mac', label: 'Mac' },
+];
+
+/** `**fett**` and `` `Code` `` -> HTML; everything else escaped first, so
+ *  nothing in the data can inject markup. */
+function rich(text: string): string {
+  const esc = keys(text).replace(/&/g, '&amp;').replace(/</g, '&lt;').replace(/>/g, '&gt;');
+  return esc.replace(/`([^`]+)`/g, '<code>$1</code>').replace(/\*\*([^*]+)\*\*/g, '<strong>$1</strong>');
+}
+
+const FORMULA_REF = referenceFor('expression').filter(
+  (e) => e.category === 'Formelfunktionen' || e.category === 'Operatoren',
+);
+
+const topic = computed(() => HELP_TOPICS.find((t) => t.id === page.value) ?? null);
+
+const plain = (s: string) => s.replace(/[`*]/g, '').toLowerCase();
+const hit = (s: string, words: string[]) => words.every((w) => plain(keys(s)).includes(w));
+
+/** Search across topics, shortcuts and functions -- every word must occur. */
+const results = computed(() => {
+  const words = query.value.toLowerCase().split(/\s+/).filter(Boolean);
+  if (!words.length) return null;
+  const items = HELP_TOPICS.flatMap((t) =>
+    t.sections.flatMap((s) =>
+      s.items
+        .filter((i) => hit(`${t.title} ${s.heading ?? ''} ${i}`, words))
+        .map((text) => ({ where: s.heading ? `${t.title} › ${s.heading}` : t.title, text })),
+    ),
+  );
+  const shortcuts = SHORTCUT_GROUPS.flatMap((g) =>
+    g.shortcuts.filter((s: Shortcut) =>
+      hit(`${g.title} ${shortcutKeys(s, 'pc')} ${shortcutKeys(s, 'mac')} ${s.description}`, words),
+    ),
+  );
+  const functions = FORMULA_REF.filter((e) => matchesQuery(e, query.value));
+  return { items, shortcuts, functions, empty: !items.length && !shortcuts.length && !functions.length };
+});
+
+/** Escape in the search box first clears a search, only then closes (an
+ *  empty box would otherwise leave it to BaseModal's own Escape handling). */
+function onSearchEscape() {
+  if (query.value) query.value = '';
+  else emit('close');
+}
+
+function go(p: Page) {
+  page.value = p;
+  query.value = '';
+}
+</script>
+
+<template>
+  <BaseModal :open="open" title="Hilfe" wide @close="emit('close')">
+    <div class="help-page">
+      <input
+        ref="searchEl"
+        v-model="query"
+        class="search"
+        type="search"
+        placeholder="Hilfe durchsuchen, z. B. „Bezug“, „fett“, „SUM“ …"
+        aria-label="Hilfe durchsuchen"
+        @keydown.esc.prevent.stop="onSearchEscape"
+      />
+
+      <div class="cols">
+        <nav class="nav">
+          <button
+            v-for="t in HELP_TOPICS"
+            :key="t.id"
+            :class="{ on: !results && page === t.id }"
+            @click="go(t.id)"
+          >
+            {{ t.title }}
+          </button>
+          <span class="sep" />
+          <button :class="{ on: !results && page === 'shortcuts' }" @click="go('shortcuts')">Tastenkürzel</button>
+          <button :class="{ on: !results && page === 'functions' }" @click="go('functions')">Funktionen</button>
+        </nav>
+
+        <div class="content">
+          <!-- search results -->
+          <template v-if="results">
+            <p v-if="results.empty" class="dim">Nichts gefunden.</p>
+            <section v-if="results.items.length">
+              <h3>Themen</h3>
+              <ul class="items">
+                <li v-for="(r, i) in results.items" :key="i">
+                  <span class="where">{{ r.where }}</span>
+                  <!-- eslint-disable-next-line vue/no-v-html -- escaped in rich() -->
+                  <span v-html="rich(r.text)" />
+                </li>
+              </ul>
+            </section>
+            <section v-if="results.shortcuts.length">
+              <h3>Tastenkürzel</h3>
+              <table class="keys">
+                <thead>
+                  <tr>
+                    <th>Aktion</th>
+                    <th v-for="c in COLUMNS" :key="c.platform" :class="{ here: c.platform === platform }">{{ c.label }}</th>
+                  </tr>
+                </thead>
+                <tr v-for="s in results.shortcuts" :key="s.keys + s.description">
+                  <td>{{ s.description }}</td>
+                  <td v-for="c in COLUMNS" :key="c.platform" :class="{ here: c.platform === platform }" :data-label="c.label">
+                    <kbd>{{ shortcutKeys(s, c.platform) }}</kbd>
+                  </td>
+                </tr>
+              </table>
+            </section>
+            <section v-if="results.functions.length">
+              <h3>Funktionen</h3>
+              <dl class="fns">
+                <template v-for="f in results.functions" :key="f.name">
+                  <dt><code>{{ f.syntax }}</code></dt>
+                  <dd>{{ f.description }}</dd>
+                </template>
+              </dl>
+            </section>
+          </template>
+
+          <!-- a topic -->
+          <template v-else-if="topic">
+            <h3 class="title">{{ topic.title }}</h3>
+            <section v-for="(s, i) in topic.sections" :key="i">
+              <h4 v-if="s.heading">{{ s.heading }}</h4>
+              <ul class="items">
+                <!-- eslint-disable-next-line vue/no-v-html -- escaped in rich() -->
+                <li v-for="(item, j) in s.items" :key="j" v-html="rich(item)" />
+              </ul>
+            </section>
+          </template>
+
+          <template v-else-if="page === 'shortcuts'">
+            <h3 class="title">Tastenkürzel</h3>
+            <p class="dim">
+              Windows und Linux verwenden dieselben Tasten. Auf dem Mac steht ⌘ für Strg und ⌥ für Alt. Viele
+              Mac-Tastaturen haben keine Tasten Pos1, Ende, Bild auf/ab und Entf, dort hilft fn. Die
+              Funktionstasten F1 bis F4 brauchen je nach Einstellung ebenfalls fn.
+            </p>
+            <section v-for="g in SHORTCUT_GROUPS" :key="g.title">
+              <h4>{{ g.title }}</h4>
+              <table class="keys">
+                <thead>
+                  <tr>
+                    <th>Aktion</th>
+                    <th v-for="c in COLUMNS" :key="c.platform" :class="{ here: c.platform === platform }">{{ c.label }}</th>
+                  </tr>
+                </thead>
+                <tr v-for="s in g.shortcuts" :key="s.keys + s.description">
+                  <td>{{ s.description }}</td>
+                  <td v-for="c in COLUMNS" :key="c.platform" :class="{ here: c.platform === platform }" :data-label="c.label">
+                    <kbd>{{ shortcutKeys(s, c.platform) }}</kbd>
+                  </td>
+                </tr>
+              </table>
+            </section>
+          </template>
+
+          <template v-else-if="page === 'functions'">
+            <h3 class="title">Funktionen</h3>
+            <p class="dim">
+              Eingebaute Funktionen und Rechenzeichen für Formeln. Argumente werden mit <code>;</code> getrennt,
+              ein <code>?</code> kennzeichnet ein optionales Argument.
+            </p>
+            <dl class="fns">
+              <template v-for="f in FORMULA_REF" :key="f.name">
+                <dt><code>{{ f.syntax }}</code></dt>
+                <dd>
+                  {{ f.description }}
+                  <span v-if="f.example" class="example">Beispiel: <code>{{ f.example }}</code></span>
+                </dd>
+              </template>
+            </dl>
+          </template>
+        </div>
+      </div>
+    </div>
+
+    <template #footer>
+      <button class="primary" @click="emit('close')">Schließen</button>
+    </template>
+  </BaseModal>
+</template>
+
+<style scoped>
+.help-page {
+  display: flex;
+  flex-direction: column;
+  gap: 12px;
+  /* fixed height: switching pages or searching must not resize (and so
+     re-centre) the dialog; the content column scrolls instead */
+  height: min(600px, calc(100dvh - 190px));
+}
+.search {
+  width: 100%;
+  box-sizing: border-box;
+  padding: 7px 10px;
+  border: 1px solid var(--border);
+  border-radius: var(--radius-sm);
+  background: var(--surface);
+  color: var(--text);
+  font: inherit;
+}
+.cols {
+  flex: 1;
+  min-height: 0;
+  display: flex;
+  gap: 18px;
+}
+.nav {
+  flex: none;
+  width: 170px;
+  display: flex;
+  flex-direction: column;
+  gap: 2px;
+  overflow-y: auto;
+}
+.nav button {
+  text-align: left;
+  border: 0;
+  background: transparent;
+  color: var(--text);
+  padding: 6px 10px;
+  border-radius: var(--radius-sm);
+  font: inherit;
+  cursor: pointer;
+}
+.nav button:hover {
+  background: var(--surface-2);
+}
+.nav button.on {
+  background: var(--accent-weak);
+  color: var(--accent);
+  font-weight: 600;
+}
+.nav .sep {
+  height: 1px;
+  background: var(--border);
+  margin: 6px 0;
+}
+.content {
+  flex: 1;
+  min-width: 0;
+  overflow-y: auto;
+  padding-right: 4px;
+  line-height: 1.5;
+}
+.title {
+  margin: 0 0 8px;
+  font-size: 15px;
+}
+h3 {
+  font-size: 13px;
+  margin: 0 0 6px;
+}
+h4 {
+  font-size: 12.5px;
+  margin: 14px 0 4px;
+  color: var(--text-dim);
+}
+section + section h3 {
+  margin-top: 16px;
+}
+.items {
+  margin: 0;
+  padding-left: 18px;
+}
+.items li + li {
+  margin-top: 4px;
+}
+.where {
+  display: block;
+  font-size: 11px;
+  color: var(--text-dim);
+}
+.keys {
+  border-collapse: collapse;
+  width: 100%;
+}
+.keys th,
+.keys td {
+  padding: 4px 8px 4px 0;
+  vertical-align: top;
+  text-align: left;
+  border-bottom: 1px solid var(--border);
+}
+.keys th {
+  font-size: 11.5px;
+  font-weight: 600;
+  color: var(--text-dim);
+}
+.keys th.here {
+  color: var(--accent);
+}
+.keys td:first-child {
+  width: 36%;
+}
+.keys td.here kbd {
+  border-color: var(--accent);
+}
+kbd {
+  font: 12px ui-monospace, SFMono-Regular, Menlo, monospace;
+  background: var(--surface-2);
+  border: 1px solid var(--border);
+  border-radius: 4px;
+  padding: 1px 5px;
+}
+.fns {
+  margin: 0;
+}
+.fns dt {
+  margin-top: 10px;
+}
+.fns dd {
+  margin: 2px 0 0 0;
+  color: var(--text-dim);
+}
+.example {
+  display: block;
+}
+code {
+  font: 12px ui-monospace, SFMono-Regular, Menlo, monospace;
+  background: var(--surface-2);
+  border-radius: 3px;
+  padding: 0 3px;
+}
+.dim {
+  color: var(--text-dim);
+}
+/* phones: navigation above the content */
+@media (max-width: 640px) {
+  .cols {
+    flex-direction: column;
+  }
+  .nav {
+    flex: none;
+    width: 100%;
+    flex-direction: row;
+    flex-wrap: wrap;
+  }
+  .nav .sep {
+    display: none;
+  }
+  /* no room for three columns: each shortcut becomes a small block, the
+     action on top, the two key columns below it with their label */
+  .keys thead {
+    display: none;
+  }
+  .keys tr {
+    display: block;
+    padding: 6px 0;
+    border-bottom: 1px solid var(--border);
+  }
+  .keys td {
+    display: block;
+    width: auto !important;
+    padding: 1px 0;
+    border: 0;
+  }
+  .keys td[data-label]::before {
+    content: attr(data-label) ': ';
+    font-size: 11px;
+    color: var(--text-dim);
+  }
+  kbd {
+    overflow-wrap: anywhere;
+  }
+}
+</style>
diff --git a/app/frontend/components/SettingsPanel.vue b/app/frontend/components/SettingsPanel.vue
index 6b207d5..b188f33 100644
--- a/app/frontend/components/SettingsPanel.vue
+++ b/app/frontend/components/SettingsPanel.vue
@@ -208,8 +208,9 @@ function resetDoc() {
             </label>
 
             <label class="f row-inline">
-              <button class="tgl" :class="{ on: selFmt.bold }" @click="applyFmt({ bold: !selFmt.bold })"><b>F</b></button>
-              <button class="tgl" :class="{ on: selFmt.italic }" @click="applyFmt({ italic: !selFmt.italic })"><i>K</i></button>
+              <button class="tgl" :class="{ on: selFmt.bold }" title="Fett (Strg+Umschalt+B)" @click="applyFmt({ bold: !selFmt.bold })"><b>F</b></button>
+              <button class="tgl" :class="{ on: selFmt.italic }" title="Kursiv (Strg+Umschalt+I)" @click="applyFmt({ italic: !selFmt.italic })"><i>K</i></button>
+              <button class="tgl" :class="{ on: selFmt.underline }" title="Unterstrichen (Strg+Umschalt+U)" @click="applyFmt({ underline: !selFmt.underline })"><u>U</u></button>
             </label>
 
             <label class="f">
diff --git a/app/frontend/components/TableGrid.vue b/app/frontend/components/TableGrid.vue
index aaf2dbd..2fd80a8 100644
--- a/app/frontend/components/TableGrid.vue
+++ b/app/frontend/components/TableGrid.vue
@@ -10,8 +10,8 @@
  * Also handles cell selection (click / shift / drag), keyboard navigation,
  * in-cell editing and per-column resize.
  */
-import { computed, nextTick, onBeforeUnmount, ref } from 'vue';
-import { numberToCol, cycleReferenceLocks } from '../engine';
+import { computed, nextTick, onBeforeUnmount, onMounted, ref, watch } from 'vue';
+import { numberToCol, cycleReferenceLocks, completeFormula } from '../engine';
 import { useDocument } from '../store/document';
 import { useLibrary } from '../store/library';
 import { DEFAULT_ROW_H, type SelectionState } from '../store/types';
@@ -116,6 +116,7 @@ function formatStyle(c: number, r: number): Record<string, string> {
   if (f.bg) s.background = f.bg;
   if (f.bold) s.fontWeight = '600';
   if (f.italic) s.fontStyle = 'italic';
+  if (f.underline) s.textDecoration = 'underline';
   return s;
 }
 
@@ -306,6 +307,21 @@ const clipMarqueeStyle = computed(() => {
     height: rowTop(k.r1 + 1) - top + 'px',
   };
 });
+/** The cell/range just picked for the formula being edited (point mode, by
+ *  mouse or arrow keys) -- the grid selection itself stays on the edited
+ *  cell meanwhile, so without this the pick would be invisible. */
+const pointRectStyle = computed(() => {
+  const k = store.pointRect.value;
+  if (!k || k.tableId !== props.tableId) return null;
+  const left = colLeft(k.c0);
+  const top = rowTop(k.r0);
+  return {
+    left: left + 'px',
+    top: top + 'px',
+    width: colLeft(k.c1 + 1) - left + 'px',
+    height: rowTop(k.r1 + 1) - top + 'px',
+  };
+});
 /** The copy/cut selection's *own* first cell, called out inside the marquee
  *  even once the live selection has moved on to pick a paste destination
  *  (which is when `is-active` no longer sits there). */
@@ -643,6 +659,81 @@ function onPointDragUp() {
   window.removeEventListener('blur', onPointDragUp);
 }
 
+// ---- references of the formula being edited (coloured, draggable) -------
+/** The edited formula's references that point into this table, outlined in
+ *  their colour. Dragging an outline's edge moves the reference, dragging a
+ *  corner resizes it -- the formula text follows live (store.moveFormulaRef),
+ *  same as Excel. */
+const refHighlights = computed(() =>
+  store.formulaRefs.value
+    .filter((h) => h.tableId === props.tableId)
+    .map((h) => {
+      const left = colLeft(h.c0);
+      const top = rowTop(h.r0);
+      return {
+        ...h,
+        style: {
+          left: left + 'px',
+          top: top + 'px',
+          width: colLeft(h.c1 + 1) - left + 'px',
+          height: rowTop(h.r1 + 1) - top + 'px',
+          '--ref': h.color,
+        },
+      };
+    }),
+);
+type RefCorner = 'nw' | 'ne' | 'sw' | 'se';
+let refDrag: {
+  index: number;
+  orig: { c0: number; r0: number; c1: number; r1: number };
+  /** null = move by the edge, else the corner being dragged */
+  corner: RefCorner | null;
+  start: { c: number; r: number };
+} | null = null;
+function onRefHandleDown(e: MouseEvent, h: { index: number; c0: number; r0: number; c1: number; r1: number }, corner: RefCorner | null) {
+  if (e.button !== 0) return;
+  e.preventDefault(); // keep focus (and the caret) in the formula editor
+  e.stopPropagation(); // no cell/canvas-object mousedown underneath
+  const start = cellFromPoint(e.clientX, e.clientY);
+  if (!start) return;
+  refDrag = { index: h.index, orig: { c0: h.c0, r0: h.r0, c1: h.c1, r1: h.r1 }, corner, start };
+  document.body.style.userSelect = 'none';
+  window.addEventListener('mousemove', onRefDragMove, true);
+  window.addEventListener('mouseup', onRefDragUp, true);
+  window.addEventListener('blur', onRefDragUp);
+}
+function onRefDragMove(e: MouseEvent) {
+  const d = refDrag;
+  const t = table.value;
+  if (!d || !t) return;
+  if (e.buttons === 0) {
+    onRefDragUp(); // a mouseup we never saw -- self-heal a stuck drag
+    return;
+  }
+  const hit = cellFromPoint(e.clientX, e.clientY);
+  if (!hit) return;
+  const o = d.orig;
+  if (!d.corner) {
+    // shift the whole rectangle, but never past the table's edges
+    const dc = Math.max(-o.c0, Math.min(t.cols - 1 - o.c1, hit.c - d.start.c));
+    const dr = Math.max(-o.r0, Math.min(t.rows - 1 - o.r1, hit.r - d.start.r));
+    store.moveFormulaRef(d.index, o.c0 + dc, o.r0 + dr, o.c1 + dc, o.r1 + dr);
+    return;
+  }
+  // the opposite corner stays put; the dragged one follows the pointer
+  const fixedC = d.corner === 'nw' || d.corner === 'sw' ? o.c1 : o.c0;
+  const fixedR = d.corner === 'nw' || d.corner === 'ne' ? o.r1 : o.r0;
+  store.moveFormulaRef(d.index, fixedC, fixedR, hit.c, hit.r);
+}
+function onRefDragUp() {
+  if (!refDrag) return;
+  refDrag = null;
+  document.body.style.userSelect = '';
+  window.removeEventListener('mousemove', onRefDragMove, true);
+  window.removeEventListener('mouseup', onRefDragUp, true);
+  window.removeEventListener('blur', onRefDragUp);
+}
+
 // ---- fill handle (drag to copy/fill, Excel/Numbers-style) ---------------
 /** Small square at the selection's bottom-right corner; dragging it repeats
  *  the selection's cells (values, formulas -- reference-adjusted like a
@@ -879,7 +970,7 @@ const editStyle = computed(() => {
   const s = editing.value;
   if (!s) return {};
   // look like the cell being edited: its own text/fill colour (else the
-  // table's), bold/italic -- a white-on-dark cell must not turn into dark
+  // table's), bold/italic/underline -- a white-on-dark cell must not turn into dark
   // text on a dark fill while editing
   const f = store.cellFormat(props.tableId, s.col, s.row);
   const style: Record<string, string> = {
@@ -892,6 +983,7 @@ const editStyle = computed(() => {
   if (f.bg) style['--surface'] = f.bg;
   if (f.bold) style.fontWeight = '600';
   if (f.italic) style.fontStyle = 'italic';
+  if (f.underline) style.textDecoration = 'underline';
   return style;
 });
 const editMirrorStyle = computed(() => {
@@ -965,7 +1057,8 @@ function commitEdit() {
   if (!editing.value) return;
   committing = true;
   const { col, row } = editing.value;
-  store.setCellInput(props.tableId, col, row, editValue.value);
+  // a forgotten closing ")" is completed rather than stored as an error
+  store.setCellInput(props.tableId, col, row, completeFormula(editValue.value));
   editing.value = null;
   store.registerFormulaEditor(null);
   autocomplete.close();
@@ -1126,6 +1219,17 @@ function onKeydown(e: KeyboardEvent) {
 
   if (mod) {
     const k = e.key.toLowerCase();
+    // Ctrl/Cmd+Shift+B (or F, "fett") / I / U: toggle bold / italic /
+    // underline for the whole selection -- on when not every selected cell
+    // has it yet, else off, same as the toggle buttons in the side panel.
+    // With Shift, so plain Cmd+B/I/U stay free for the browser/OS.
+    const toggles: Record<string, 'bold' | 'italic' | 'underline'> = { b: 'bold', f: 'bold', i: 'italic', u: 'underline' };
+    const toggle = e.shiftKey ? toggles[k] : undefined;
+    if (toggle) {
+      e.preventDefault();
+      e.stopPropagation();
+      return store.applySelectionFormat({ [toggle]: !store.selectionFormat.value[toggle] });
+    }
     if (k === 'a') {
       e.preventDefault();
       e.stopPropagation();
@@ -1347,10 +1451,25 @@ function onFocusGridRequest(e: Event) {
 }
 window.addEventListener('numolus:focus-grid', onFocusGridRequest);
 
+// After a reload (or opening a document / switching sheets) the restored
+// selection is visible but nothing had the keyboard, so arrow keys and typing
+// went nowhere until the user clicked. Take it whenever the selection sits in
+// this table and the keyboard is otherwise unclaimed -- never away from an
+// input, the formula bar or another table someone is working in.
+function claimIdleKeyboard() {
+  if (!mine.value || !root.value) return;
+  const active = document.activeElement;
+  if (active && active !== document.body) return;
+  root.value.focus({ preventScroll: true });
+}
+onMounted(claimIdleKeyboard);
+watch(() => mine.value?.tableId, claimIdleKeyboard, { flush: 'post' });
+
 onBeforeUnmount(() => {
   window.removeEventListener('numolus:focus-grid', onFocusGridRequest);
   onDragUp();
   onPointDragUp();
+  onRefDragUp();
   onFillDragUp();
   onResizeUp();
   onRowResizeUp();
@@ -1456,6 +1575,25 @@ defineExpose({
       </div>
       <div v-if="clipMarqueeStyle" class="clip-marquee" :style="clipMarqueeStyle" />
       <div v-if="clipAnchorStyle" class="clip-anchor" :style="clipAnchorStyle" />
+      <div v-for="h in refHighlights" :key="'ref' + h.index" class="ref-hl" :style="h.style">
+        <template v-if="!h.whole">
+          <span
+            v-for="edge in ['top', 'right', 'bottom', 'left']"
+            :key="edge"
+            class="ref-edge"
+            :class="'ref-edge-' + edge"
+            @mousedown="onRefHandleDown($event, h, null)"
+          />
+          <span
+            v-for="corner in (['nw', 'ne', 'sw', 'se'] as const)"
+            :key="corner"
+            class="ref-corner"
+            :class="'ref-corner-' + corner"
+            @mousedown="onRefHandleDown($event, h, corner)"
+          />
+        </template>
+      </div>
+      <div v-if="pointRectStyle" class="point-rect" :style="pointRectStyle" />
       <div v-if="fillPreviewStyle" class="fill-preview" :style="fillPreviewStyle" />
       <div
         v-if="fillHandleStyle"
@@ -1666,6 +1804,84 @@ defineExpose({
   box-shadow: inset 0 0 0 2px var(--accent);
   z-index: 8;
 }
+/* the reference being picked for a formula (point mode) */
+.point-rect {
+  position: absolute;
+  pointer-events: none;
+  border: 2px dashed var(--accent);
+  background: var(--accent-weak);
+  box-sizing: border-box;
+  z-index: 8;
+}
+/* a reference of the formula being edited, in its colour (Excel-style) */
+.ref-hl {
+  position: absolute;
+  pointer-events: none; /* the inside stays clickable for picking cells */
+  border: 2px solid var(--ref);
+  background: color-mix(in srgb, var(--ref) 10%, transparent);
+  box-sizing: border-box;
+  z-index: 9;
+}
+/* the edges move the reference, the corners resize it */
+.ref-edge {
+  position: absolute;
+  pointer-events: auto;
+  cursor: move;
+}
+.ref-edge-top,
+.ref-edge-bottom {
+  left: 0;
+  right: 0;
+  height: 6px;
+}
+.ref-edge-top {
+  top: -4px;
+}
+.ref-edge-bottom {
+  bottom: -4px;
+}
+.ref-edge-left,
+.ref-edge-right {
+  top: 0;
+  bottom: 0;
+  width: 6px;
+}
+.ref-edge-left {
+  left: -4px;
+}
+.ref-edge-right {
+  right: -4px;
+}
+.ref-corner {
+  position: absolute;
+  pointer-events: auto;
+  width: 7px;
+  height: 7px;
+  background: var(--ref);
+  border: 1px solid var(--surface);
+  border-radius: 1px;
+  z-index: 1;
+}
+.ref-corner-nw {
+  left: -5px;
+  top: -5px;
+  cursor: nwse-resize;
+}
+.ref-corner-ne {
+  right: -5px;
+  top: -5px;
+  cursor: nesw-resize;
+}
+.ref-corner-sw {
+  left: -5px;
+  bottom: -5px;
+  cursor: nesw-resize;
+}
+.ref-corner-se {
+  right: -5px;
+  bottom: -5px;
+  cursor: nwse-resize;
+}
 /* small square at the selection's bottom-right corner -- drag to fill/copy */
 .fill-handle {
   position: absolute;
diff --git a/app/frontend/data/__tests__/help.spec.ts b/app/frontend/data/__tests__/help.spec.ts
new file mode 100644
index 0000000..bbbd295
--- /dev/null
+++ b/app/frontend/data/__tests__/help.spec.ts
@@ -0,0 +1,56 @@
+import { describe, expect, it } from 'vitest';
+import { HELP_TOPICS, SHORTCUT_GROUPS, shortcutKeys } from '../help';
+
+describe('in-app help content', () => {
+  it('topics have unique ids that never clash with the fixed pages', () => {
+    const ids = HELP_TOPICS.map((t) => t.id);
+    expect(new Set(ids).size).toBe(ids.length);
+    expect(ids).not.toContain('shortcuts');
+    expect(ids).not.toContain('functions');
+  });
+
+  it('no empty topics, sections, items or shortcuts', () => {
+    for (const t of HELP_TOPICS) {
+      expect(t.title.trim()).not.toBe('');
+      expect(t.sections.length).toBeGreaterThan(0);
+      for (const s of t.sections) {
+        expect(s.items.length).toBeGreaterThan(0);
+        for (const i of s.items) expect(i.trim()).not.toBe('');
+      }
+    }
+    for (const g of SHORTCUT_GROUPS) {
+      expect(g.shortcuts.length).toBeGreaterThan(0);
+      for (const s of g.shortcuts) {
+        expect(s.keys.trim()).not.toBe('');
+        expect(s.description.trim()).not.toBe('');
+      }
+    }
+  });
+
+  it('inline markup is balanced, so nothing renders half-bold', () => {
+    const all = HELP_TOPICS.flatMap((t) => t.sections.flatMap((s) => s.items));
+    for (const text of all) {
+      expect((text.match(/`/g) ?? []).length % 2, text).toBe(0);
+      expect((text.match(/\*\*/g) ?? []).length % 2, text).toBe(0);
+    }
+  });
+
+  it('names the keys per platform: Strg on Windows/Linux, ⌘/⌥ and the Mac overrides on a Mac', () => {
+    expect(shortcutKeys({ keys: 'Mod+Umschalt+U' }, 'pc')).toBe('Strg+Umschalt+U');
+    expect(shortcutKeys({ keys: 'Mod+Umschalt+U' }, 'mac')).toBe('⌘+Umschalt+U');
+    expect(shortcutKeys({ keys: 'Alt+Enter oder Mod+Enter' }, 'mac')).toBe('⌥+Enter oder ⌘+Enter');
+    expect(shortcutKeys({ keys: 'Pos1 / Ende', mac: 'fn+← / fn+→' }, 'pc')).toBe('Pos1 / Ende');
+    expect(shortcutKeys({ keys: 'Pos1 / Ende', mac: 'fn+← / fn+→' }, 'mac')).toBe('fn+← / fn+→');
+    // running text: only whole words are key names
+    expect(shortcutKeys('Alter mit Mod', 'mac')).toBe('Alter mit ⌘');
+  });
+
+  it('no Windows/Linux key text is left with a Mac-only symbol, and vice versa', () => {
+    for (const g of SHORTCUT_GROUPS) {
+      for (const s of g.shortcuts) {
+        expect(shortcutKeys(s, 'pc'), s.keys).not.toMatch(/[⌘⌥⌫]|\bfn\b/);
+        expect(shortcutKeys(s, 'mac'), s.keys).not.toMatch(/\b(Strg|Mod|Alt)\b/);
+      }
+    }
+  });
+});
diff --git a/app/frontend/data/help.ts b/app/frontend/data/help.ts
new file mode 100644
index 0000000..5999516
--- /dev/null
+++ b/app/frontend/data/help.ts
@@ -0,0 +1,231 @@
+/**
+ * Content of the in-app help (components/HelpModal.vue): user-facing topics
+ * and the keyboard shortcuts. Kept as plain data so the dialog's search can
+ * run over it; the formula functions are not listed here but taken from
+ * data/codeReference.ts, so a new built-in shows up in the help by itself.
+ *
+ * Text may use `**fett**` and `` `Code` `` -- see HelpModal's `rich()`.
+ * Hand-maintained: whoever adds or changes a shortcut or a visible feature
+ * updates this file too (the shortcut test only checks its shape).
+ */
+
+export interface HelpSection {
+  heading?: string;
+  items: string[];
+}
+
+export interface HelpTopic {
+  id: string;
+  title: string;
+  sections: HelpSection[];
+}
+
+export interface Shortcut {
+  /** As on Windows and Linux, with `Mod` for the platform's command key --
+   *  see {@link shortcutKeys}. */
+  keys: string;
+  /** Mac keys where they differ by more than ⌘/⌥ (no Pos1/Bild/Entf keys on
+   *  most Mac keyboards, F-keys behind fn, trackpad gestures). */
+  mac?: string;
+  description: string;
+}
+
+export type KeyPlatform = 'pc' | 'mac';
+
+/** The keys of a shortcut as written on the given platform: `Mod` is Strg on
+ *  Windows/Linux and ⌘ on a Mac, `Alt` is ⌥ on a Mac. Text that is not a key
+ *  name (e.g. "Mod" in a help topic) is converted the same way. */
+export function shortcutKeys(s: Pick<Shortcut, 'keys' | 'mac'> | string, platform: KeyPlatform): string {
+  const text = typeof s === 'string' ? s : platform === 'mac' ? (s.mac ?? s.keys) : s.keys;
+  if (platform === 'pc') return text.replace(/\bMod\b/g, 'Strg');
+  return text.replace(/\bMod\b/g, '⌘').replace(/\bAlt\b/g, '⌥');
+}
+
+export interface ShortcutGroup {
+  title: string;
+  shortcuts: Shortcut[];
+}
+
+export const HELP_TOPICS: HelpTopic[] = [
+  {
+    id: 'start',
+    title: 'Erste Schritte',
+    sections: [
+      {
+        items: [
+          'Ein **Blatt** ist eine freie Fläche, auf der **Objekte** liegen: Tabellen, Diagramme, Textfelder und Buttons. Sie werden über die Symbole in der Werkzeugleiste eingefügt.',
+          'Objekte an ihrer Kopfleiste verschieben, an der Ecke unten rechts in der Größe ändern. Ein Doppelklick auf den Namen benennt sie um, das `×` in der Kopfleiste löscht sie.',
+          'Mehrere Blätter über die Reiter unten: hinzufügen mit `+`, umbenennen per Doppelklick, Reihenfolge durch Ziehen.',
+          'Das Zahnrad neben dem Titel öffnet die **Einstellungen** für das gewählte Objekt, das Blatt und das Dokument.',
+          'Zoomen mit `Mod` + Mausrad oder über die Zoom-Leiste unten rechts.',
+        ],
+      },
+    ],
+  },
+  {
+    id: 'tables',
+    title: 'Tabellen & Auswahl',
+    sections: [
+      {
+        heading: 'Auswählen',
+        items: [
+          'Klick wählt eine Zelle, **Umschalt+Klick** oder Ziehen einen Bereich.',
+          'Klick auf einen Spalten- oder Zeilenkopf wählt die ganze Spalte oder Zeile, die Ecke oben links die ganze Tabelle.',
+          '**Mod+Klick** fügt eine weitere Zelle hinzu, **Mod+Ziehen** einen weiteren Bereich.',
+          '**Mod+A** wählt den zusammenhängenden Bereich um die aktive Zelle, ein zweites Mal alle befüllten Zellen.',
+          'Die Statusleiste zeigt Summe, Mittelwert und Anzahl der Auswahl.',
+        ],
+      },
+      {
+        heading: 'Eingeben',
+        items: [
+          'Einfach lostippen oder **F2** bzw. Doppelklick, um den Inhalt zu bearbeiten. **Enter** übernimmt, **Escape** bricht ab.',
+          'Zeilenumbruch in einer Zelle mit **Alt+Enter** oder **Mod+Enter**.',
+          'Der Inhalt der aktiven Zelle steht auch in der **Formelleiste** oben und kann dort bearbeitet werden. Links daneben zeigt das Namensfeld, wo man sich befindet. Dort kann auch ein Ziel eingegeben werden (`B5`, `Umsatz::A1:C4`, ein Tabellen- oder Blattname).',
+        ],
+      },
+      {
+        heading: 'Zeilen & Spalten',
+        items: [
+          'Rechtsklick auf einen Zeilen- oder Spaltenkopf: einfügen oder löschen.',
+          'Rechtsklick in eine Zelle: kopieren, einfügen, Zeile oder Spalte am Ende hinzufügen, Abhängigkeiten anzeigen.',
+          'Spaltenbreite und Zeilenhöhe durch Ziehen am Rand des Kopfs.',
+          'In den Einstellungen kann eine Tabelle eine **feste Größe** mit eigenem Scrollbereich und fixierten Kopfzeilen und Spalten bekommen.',
+        ],
+      },
+    ],
+  },
+  {
+    id: 'formulas',
+    title: 'Formeln',
+    sections: [
+      {
+        heading: 'Grundlagen',
+        items: [
+          'Eine Formel beginnt mit `=`, z. B. `=SUM(B2:B6)*1.1` oder `=B2+C2`. Argumente werden mit `;` getrennt.',
+          'Bezüge: `A1` eine Zelle, `A1:C4` ein Bereich, `B:B` eine ganze Spalte, `2:2` eine ganze Zeile.',
+          'Andere Tabelle: `Umsatz!B2` oder `Umsatz::B2`. Gibt es den Tabellennamen auf mehreren Blättern: `Analyse!Umsatz::B2`. Namen mit Leerzeichen in einfachen Anführungszeichen: `\'Kosten Q3\'!A1`.',
+          'Text in doppelten Anführungszeichen: `="Summe: " & B7`.',
+          'Fehlt beim Übernehmen mit Enter eine schließende Klammer, wird sie ergänzt.',
+        ],
+      },
+      {
+        heading: 'Bezüge zeigen statt tippen',
+        items: [
+          'Während der Eingabe einer Formel fügt ein Klick in eine Zelle ihren Bezug ein, Ziehen einen Bereich. Das geht auch in anderen Tabellen.',
+          'Mit der Tastatur: Direkt nach `=`, `(`, `;` oder einem Rechenzeichen wählen die **Pfeiltasten** eine Zelle, mit **Umschalt** einen Bereich.',
+          'Alle Bezüge der Formel werden farbig umrahmt. **Am Rand ziehen** verschiebt einen Bezug, **an einer Ecke ziehen** ändert seine Größe. Die Formel passt sich sofort an.',
+          '**F4** schaltet den Bezug am Cursor durch: `A1` → `$A$1` → `A$1` → `$A1`. Ein `$` hält Spalte oder Zeile beim Kopieren fest.',
+        ],
+      },
+      {
+        heading: 'Funktionen',
+        items: [
+          'Beim Tippen eines Funktionsnamens erscheint eine Vorschlagsliste. **Pfeil auf/ab** wählt, **Tab** oder **Enter** übernimmt.',
+          'Alle eingebauten Funktionen stehen unter **Funktionen** in dieser Hilfe.',
+          '**Eigene Funktionen** legt man über `fx` in der Werkzeugleiste an. Sie werden danach wie eingebaute aufgerufen.',
+          '**Benannte Bereiche** (Etikett-Symbol) geben einem Bereich einen Namen, z. B. `=SUM(Umsatz_Q1)`.',
+          'Rechtsklick in eine Zelle › **Abhängigkeiten anzeigen** zeigt, woraus eine Formel rechnet und wer sie verwendet.',
+        ],
+      },
+    ],
+  },
+  {
+    id: 'format',
+    title: 'Formatierung',
+    sections: [
+      {
+        items: [
+          'Zellen auswählen, dann in den Einstellungen unter **Auswahl**: Ausrichtung, Zahlenformat, **F**ett, **K**ursiv, **U**nterstrichen, Text- und Füllfarbe.',
+          'Mit der Tastatur: **Mod+Umschalt+B** (oder **F**) fett, **Mod+Umschalt+I** kursiv, **Mod+Umschalt+U** unterstrichen. Erneut drücken schaltet wieder aus.',
+          'Die Formatierung gilt für die ganze Auswahl, auch für mehrere Bereiche.',
+          'Wie Zahlen dargestellt werden (Dezimal- und Tausendertrennzeichen), richtet sich nach der Ländereinstellung von Objekt, Blatt oder Dokument.',
+        ],
+      },
+    ],
+  },
+  {
+    id: 'macros',
+    title: 'Makros & Buttons',
+    sections: [
+      {
+        items: [
+          '**Makros** (Symbol in der Werkzeugleiste) ändern per Skript Zellen, Zeilen, Spalten, Tabellen und Blätter, auch dokumentweit.',
+          'Ein Makro läuft nur, wenn man es startet: mit **Ausführen** im Makro-Dialog oder per Klick auf ein **Button**-Objekt auf der Fläche.',
+          'Welches Makro ein Button startet, wird in den Einstellungen oder per Rechtsklick auf den Button gewählt.',
+          'Neben dem Editor steht eine durchsuchbare Befehlsreferenz. Ein Klick fügt den Befehl ein.',
+        ],
+      },
+    ],
+  },
+  {
+    id: 'files',
+    title: 'Speichern & Teilen',
+    sections: [
+      {
+        heading: 'Speichern',
+        items: [
+          'Ohne Anmeldung liegen Dokumente **in diesem Browser** und werden automatisch gespeichert. In einem anderen Browser oder nach dem Löschen der Browserdaten sind sie dort nicht vorhanden.',
+          'Mit **Anmelden** (Link oder Code per E-Mail) liegen Dokumente im Konto und sind überall verfügbar.',
+          '**Datei › Dokumente …** listet alle Dokumente: öffnen, umbenennen, duplizieren, löschen, ins Konto hochladen.',
+          '**Datei** öffnet und importiert `.num`, `.json`, `.csv` und `.xlsx` und exportiert in diese Formate.',
+        ],
+      },
+      {
+        heading: 'Teilen & gemeinsam bearbeiten',
+        items: [
+          '**Teilen** erstellt einen Link zum Ansehen oder Bearbeiten oder lädt per E-Mail ein. Ein lokales Dokument wird dafür zuerst hochgeladen.',
+          'Änderungen der anderen erscheinen sofort. Ihre Auswahl ist als farbiger Rahmen mit Namen zu sehen, oben rechts stehen ihre Avatare.',
+          'Rückgängig nimmt nur die eigenen Änderungen zurück.',
+          'Wer nur ansehen darf, sieht „Nur Lesen“ und kann nichts ändern.',
+        ],
+      },
+    ],
+  },
+];
+
+export const SHORTCUT_GROUPS: ShortcutGroup[] = [
+  {
+    title: 'In der Tabelle',
+    shortcuts: [
+      { keys: 'Pfeiltasten', description: 'Zelle wechseln' },
+      { keys: 'Umschalt+Pfeiltasten', description: 'Auswahl erweitern' },
+      { keys: 'Mod+Pfeiltasten', description: 'An den Rand des Datenblocks springen (mit Umschalt: Auswahl bis dorthin)' },
+      { keys: 'Tab / Umschalt+Tab', description: 'Nach rechts / links, innerhalb einer Auswahl der Reihe nach' },
+      { keys: 'Enter / Umschalt+Enter', description: 'Nach unten / oben, innerhalb einer Auswahl der Reihe nach' },
+      { keys: 'Pos1 / Ende', mac: 'fn+← / fn+→', description: 'Anfang / Ende der Zeile' },
+      { keys: 'Mod+Pos1 / Mod+Ende', mac: 'fn+⌘+← / fn+⌘+→', description: 'Erste / letzte Zelle der Tabelle' },
+      { keys: 'Bild auf / Bild ab', mac: 'fn+↑ / fn+↓', description: 'Seitenweise blättern' },
+      { keys: 'Mod+A', description: 'Zusammenhängenden Bereich wählen, zweimal: alle befüllten Zellen' },
+      { keys: 'F2', mac: 'F2 (ggf. fn+F2)', description: 'Aktive Zelle bearbeiten (oder einfach lostippen)' },
+      { keys: 'Entf / Rücktaste', mac: '⌫ / fn+⌫', description: 'Inhalt der Auswahl leeren' },
+      { keys: 'Mod+C / Mod+X / Mod+V', description: 'Kopieren / Ausschneiden / Einfügen' },
+      { keys: 'Escape', description: 'Markierung der kopierten Zellen aufheben' },
+      { keys: 'Mod+Umschalt+B oder F', description: 'Fett ein/aus' },
+      { keys: 'Mod+Umschalt+I', description: 'Kursiv ein/aus' },
+      { keys: 'Mod+Umschalt+U', description: 'Unterstrichen ein/aus' },
+    ],
+  },
+  {
+    title: 'Beim Bearbeiten einer Zelle',
+    shortcuts: [
+      { keys: 'Enter / Tab', description: 'Übernehmen und nach unten / rechts' },
+      { keys: 'Umschalt+Enter / Umschalt+Tab', description: 'Übernehmen und nach oben / links' },
+      { keys: 'Escape', description: 'Abbrechen' },
+      { keys: 'Alt+Enter oder Mod+Enter', description: 'Zeilenumbruch in der Zelle' },
+      { keys: 'Pfeiltasten nach = ( ; oder Rechenzeichen', description: 'Zellbezug wählen, mit Umschalt einen Bereich' },
+      { keys: 'F4', mac: 'F4 (ggf. fn+F4)', description: 'Bezug sperren: A1 → $A$1 → A$1 → $A1' },
+      { keys: 'Pfeil auf/ab, Tab oder Enter', description: 'In der Vorschlagsliste wählen und übernehmen' },
+    ],
+  },
+  {
+    title: 'Allgemein',
+    shortcuts: [
+      { keys: 'Mod+Z', description: 'Rückgängig' },
+      { keys: 'Mod+Y oder Mod+Umschalt+Z', description: 'Wiederholen' },
+      { keys: 'Mod+Mausrad', mac: '⌘+Mausrad oder Trackpad mit zwei Fingern auseinander/zusammen', description: 'Zoomen' },
+      { keys: 'Entf / Rücktaste', mac: '⌫', description: 'Gewähltes Diagramm löschen' },
+      { keys: 'F1', mac: 'F1 (ggf. fn+F1)', description: 'Diese Hilfe öffnen' },
+    ],
+  },
+];
diff --git a/app/frontend/engine/__tests__/parser.spec.ts b/app/frontend/engine/__tests__/parser.spec.ts
index d17b28f..a0e4182 100644
--- a/app/frontend/engine/__tests__/parser.spec.ts
+++ b/app/frontend/engine/__tests__/parser.spec.ts
@@ -1,6 +1,7 @@
 import { describe, it, expect } from 'vitest';
 import {
   parseFormula,
+  completeFormula,
   parseFunctionBlock,
   parseMacroBlock,
   collectRefs,
@@ -489,3 +490,21 @@ describe('collectRefsInBlock -- reference walk used by the macro save-time quali
     expect(refs).toHaveLength(2);
   });
 });
+
+describe('completeFormula -- closing what Enter left open', () => {
+  it('appends missing closing parentheses', () => {
+    expect(completeFormula('=SUMME(A1:A5')).toBe('=SUMME(A1:A5)');
+    expect(completeFormula('=RUNDEN(SUMME(A1;B1)*(2+3')).toBe('=RUNDEN(SUMME(A1;B1)*(2+3))');
+    expect(completeFormula('=SUMME(A1 ')).toBe('=SUMME(A1 )');
+  });
+  it('closes an open text literal before the parentheses', () => {
+    expect(completeFormula('=WENN(A1>0;"ja')).toBe('=WENN(A1>0;"ja")');
+  });
+  it('leaves valid formulas, plain text and unfixable input alone', () => {
+    expect(completeFormula('=SUMME(A1:A5)')).toBe('=SUMME(A1:A5)');
+    expect(completeFormula('Hallo (Welt')).toBe('Hallo (Welt');
+    expect(completeFormula('=SUMME(A1+')).toBe('=SUMME(A1+');
+    expect(completeFormula('=A1)')).toBe('=A1)');
+    expect(completeFormula('=(')).toBe('=(');
+  });
+});
diff --git a/app/frontend/engine/__tests__/refs.spec.ts b/app/frontend/engine/__tests__/refs.spec.ts
index 2462ba2..b59aa28 100644
--- a/app/frontend/engine/__tests__/refs.spec.ts
+++ b/app/frontend/engine/__tests__/refs.spec.ts
@@ -1,5 +1,5 @@
 import { describe, it, expect } from 'vitest';
-import { parseA1, toA1, cycleReferenceLocks, currentIdentifierAtCaret } from '../refs';
+import { parseA1, toA1, cycleReferenceLocks, currentIdentifierAtCaret, formulaRefSpans } from '../refs';
 
 describe('parseA1 / toA1: $-locked (absolute/mixed) references', () => {
   it('parseA1 reports which axes are $-locked', () => {
@@ -121,3 +121,30 @@ describe('currentIdentifierAtCaret -- function-name autocomplete detection', ()
     expect(currentIdentifierAtCaret('=SUM("x', 7)).toBeNull();
   });
 });
+
+describe('formulaRefSpans -- references with their position in the text', () => {
+  const texts = (f: string) => formulaRefSpans(f).map((s) => f.slice(s.start, s.end));
+
+  it('finds cells, ranges and whole lines in text order', () => {
+    expect(texts('=SUMME(A1:B3;$C$2)*D4+B:B')).toEqual(['A1:B3', '$C$2', 'D4', 'B:B']);
+    const [r] = formulaRefSpans('=A1:$B$3');
+    expect(r.a).toEqual({ col: 0, row: 0, colAbs: false, rowAbs: false });
+    expect(r.b).toEqual({ col: 1, row: 2, colAbs: true, rowAbs: true });
+    expect(formulaRefSpans('=2:5')[0]).toMatchObject({ whole: 'row', a: { row: 1 }, b: { row: 4 } });
+  });
+
+  it('includes the qualifier in the span and reports it separately', () => {
+    const f = "='Kosten Q3'!A1+Analyse!Umsatz::B2:C4";
+    expect(texts(f)).toEqual(["'Kosten Q3'!A1", 'Analyse!Umsatz::B2:C4']);
+    const [q, s] = formulaRefSpans(f);
+    expect(q).toMatchObject({ qualifier: 'Kosten Q3', refStart: f.indexOf('A1') });
+    expect(s).toMatchObject({ qualifier: 'Umsatz', sheetQualifier: 'Analyse' });
+  });
+
+  it('skips function names, strings and named ranges; tolerates unfinished input', () => {
+    expect(texts('=LOG10(A1)&"B2"&Umsatz_Q1')).toEqual(['A1']);
+    expect(texts('=SUMME(A1:A5;B')).toEqual(['A1:A5']);
+    expect(texts('=WENN(A1;"offen')).toEqual([]);
+    expect(texts('A1')).toEqual([]);
+  });
+});
diff --git a/app/frontend/engine/index.ts b/app/frontend/engine/index.ts
index 476baff..b37b779 100644
--- a/app/frontend/engine/index.ts
+++ b/app/frontend/engine/index.ts
@@ -8,6 +8,7 @@
 export { tokenize, LexError, type Token, type TokenType } from './lexer';
 export {
   parseFormula,
+  completeFormula,
   parseFunctionBlock,
   parseMacroBlock,
   collectRefs,
@@ -37,6 +38,8 @@ export {
   WHOLE_LINE_END,
   cycleReferenceLocks,
   currentIdentifierAtCaret,
+  formulaRefSpans,
+  type RefSpan,
 } from './refs';
 export {
   Workbook,
diff --git a/app/frontend/engine/parser.ts b/app/frontend/engine/parser.ts
index 0626980..2a83004 100644
--- a/app/frontend/engine/parser.ts
+++ b/app/frontend/engine/parser.ts
@@ -763,6 +763,53 @@ export function parseFormula(src: string, paramNames?: readonly string[]): Node
   return new Parser(toks, paramNames, paramNames === undefined).parse();
 }
 
+/**
+ * Repair the one mistake that is almost always just forgotten typing: a
+ * formula committed with Enter while parentheses (or a "..." text literal)
+ * are still open, e.g. `=SUMME(A1:A5` or `=WENN(A1>0;"ja`. Same as Excel and
+ * Numbers, the missing closers are appended at the end.
+ *
+ * Deliberately conservative: anything that already parses, isn't a formula,
+ * or still doesn't parse after closing (`=SUMME(A1;`, a stray `)` too many)
+ * comes back unchanged, so the cell shows its usual parse error instead of a
+ * "repair" that guessed something the user never meant.
+ */
+export function completeFormula(input: string): string {
+  if (!input.startsWith('=')) return input;
+  const parses = (src: string) => {
+    try {
+      parseFormula(src);
+      return true;
+    } catch {
+      return false;
+    }
+  };
+  if (parses(input)) return input;
+
+  let fixed = input;
+  let toks: Token[];
+  try {
+    toks = tokenize(fixed.slice(1));
+  } catch (e) {
+    // an unterminated "..." literal swallows everything up to the end, so
+    // closing it first is the only way to count the parentheses before it
+    if (!(e instanceof LexError) || !e.message.startsWith('Unterminated string')) return input;
+    fixed += '"';
+    try {
+      toks = tokenize(fixed.slice(1));
+    } catch {
+      return input;
+    }
+  }
+  let depth = 0;
+  for (const t of toks) {
+    if (t.type === 'LPAREN') depth++;
+    else if (t.type === 'RPAREN' && --depth < 0) return input;
+  }
+  fixed += ')'.repeat(depth);
+  return fixed !== input && parses(fixed) ? fixed : input;
+}
+
 /**
  * Parse a "block" function body -- the statement grammar (assignments,
  * `FOR`/`DO`/`END`, `IF`/`THEN`/`ELSE`/`END`, `RETURN` anywhere) used by a
diff --git a/app/frontend/engine/refs.ts b/app/frontend/engine/refs.ts
index bdae6c7..df90c7d 100644
--- a/app/frontend/engine/refs.ts
+++ b/app/frontend/engine/refs.ts
@@ -174,6 +174,102 @@ export function currentIdentifierAtCaret(
   return { text: last.value, start: last.pos + 1 };
 }
 
+/** One cell/range reference found in a formula's text -- see {@link formulaRefSpans}. */
+export interface RefSpan {
+  /** offsets into the formula (including its leading "="): `start` is where
+   *  the qualifier (if any) begins, `refStart` where the A1 part begins */
+  start: number;
+  refStart: number;
+  end: number;
+  qualifier: string | null;
+  sheetQualifier?: string;
+  /** both corners as written (`end` equals `start` for a single cell) */
+  a: { col: number; row: number; colAbs: boolean; rowAbs: boolean };
+  b: { col: number; row: number; colAbs: boolean; rowAbs: boolean };
+  /** a whole-column/whole-row range (`B:B`, `2:5`); its open axis runs to
+   *  {@link WHOLE_LINE_END} */
+  whole?: LineAxis;
+}
+
+/**
+ * Every cell/range reference in a formula, in text order, with where it sits
+ * in the text -- what the grid colours while a formula is edited (and lets
+ * the user drag to change it, Excel-style). Same token-level reading of the
+ * `reference` grammar rule the parser applies (optional `Blatt!Tabelle::` /
+ * `Tabelle!` qualifier, `A1`, `A1:B2`, `B:B`), but tolerant: an incomplete
+ * formula still yields the references written so far. Named ranges are left
+ * out (they have no position of their own to drag); a formula that doesn't
+ * even tokenize (open "..." literal) yields nothing.
+ */
+export function formulaRefSpans(formula: string): RefSpan[] {
+  if (!formula.startsWith('=')) return [];
+  let toks: Token[];
+  try {
+    toks = tokenize(formula.slice(1));
+  } catch {
+    return [];
+  }
+  const isName = (t: Token | undefined) => !!t && (t.type === 'IDENT' || t.type === 'QUOTED');
+  const out: RefSpan[] = [];
+  let i = 0;
+  while (i < toks.length) {
+    const first = toks[i];
+    let j = i;
+    let qualifier: string | null = null;
+    let sheetQualifier: string | undefined;
+    if (isName(toks[j]) && toks[j + 1]?.type === 'BANG' && isName(toks[j + 2]) && toks[j + 3]?.type === 'DBLCOLON') {
+      sheetQualifier = toks[j].value;
+      qualifier = toks[j + 2].value;
+      j += 4;
+    } else if (isName(toks[j]) && (toks[j + 1]?.type === 'BANG' || toks[j + 1]?.type === 'DBLCOLON')) {
+      qualifier = toks[j].value;
+      j += 2;
+    }
+    const line = wholeLineAt(toks, j);
+    const cell = toks[j];
+    if (line) {
+      const max = WHOLE_LINE_END;
+      const isCol = line.axis === 'col';
+      out.push({
+        start: first.pos + 1,
+        refStart: line.a.pos + 1,
+        end: line.b.pos + line.b.value.length + 1,
+        qualifier,
+        sheetQualifier,
+        a: { col: isCol ? line.start : 0, row: isCol ? 0 : line.start, colAbs: isCol && line.startAbs, rowAbs: !isCol && line.startAbs },
+        b: { col: isCol ? line.end : max, row: isCol ? max : line.end, colAbs: isCol && line.endAbs, rowAbs: !isCol && line.endAbs },
+        whole: line.axis,
+      });
+      i = j + 3;
+      continue;
+    }
+    if (cell?.type === 'IDENT' && looksLikeCell(cell.value) && toks[j + 1]?.type !== 'LPAREN') {
+      const a = parseA1(cell.value);
+      let last = cell;
+      let b = a;
+      const other = toks[j + 2];
+      if (toks[j + 1]?.type === 'COLON' && other?.type === 'IDENT' && looksLikeCell(other.value)) {
+        b = parseA1(other.value);
+        last = other;
+        j += 2;
+      }
+      out.push({
+        start: first.pos + 1,
+        refStart: cell.pos + 1,
+        end: last.pos + last.value.length + 1,
+        qualifier,
+        sheetQualifier,
+        a,
+        b,
+      });
+      i = j + 1;
+      continue;
+    }
+    i++;
+  }
+  return out;
+}
+
 // ---- whole-column / whole-row references (`B:B`, `A:C`, `1:1`, `$2:$5`) ----
 
 /** Stand-in for "the last row/column" in a whole-column/whole-row range's
diff --git a/app/frontend/io/json.ts b/app/frontend/io/json.ts
index 810854d..12ca866 100644
--- a/app/frontend/io/json.ts
+++ b/app/frontend/io/json.ts
@@ -171,6 +171,7 @@ function normaliseCellFormat(x: unknown): CellFormat | undefined {
   if (colorOrUndef(f.bg)) out.bg = f.bg;
   if (f.bold === true) out.bold = true;
   if (f.italic === true) out.italic = true;
+  if (f.underline === true) out.underline = true;
   return Object.keys(out).length ? out : undefined;
 }
 function normaliseFormats(x: unknown): Record<string, CellFormat> | undefined {
diff --git a/app/frontend/store/__tests__/document.spec.ts b/app/frontend/store/__tests__/document.spec.ts
index d7b1093..fe8e7e6 100644
--- a/app/frontend/store/__tests__/document.spec.ts
+++ b/app/frontend/store/__tests__/document.spec.ts
@@ -1,4 +1,5 @@
 import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
+import { ref } from 'vue';
 import { useDocument, type DocumentStore } from '../document';
 import { isError, toA1 } from '../../engine';
 import { serializeDocument, parseDocument } from '../../io/json';
@@ -489,6 +490,16 @@ describe('cell formatting, number formats, row height', () => {
     expect(s.tableById(id)!.rowHeights).toBeUndefined();
   });
 
+  it('underline is a cell format like bold and survives a JSON round-trip', () => {
+    const s = fresh();
+    const id = tableId(s, 'Umsatz');
+    s.setRangeFormat(id, { col: 0, row: 0 }, { col: 1, row: 1 }, { underline: true, italic: true });
+    s.replaceDocument(parseDocument(serializeDocument(s.snapshot())));
+    expect(s.cellFormat(id, 1, 1)).toEqual({ underline: true, italic: true });
+    s.setRangeFormat(id, { col: 0, row: 0 }, { col: 1, row: 1 }, { underline: false });
+    expect(s.cellFormat(id, 0, 0)).toEqual({ italic: true });
+  });
+
   it('formatting + row heights survive a JSON round-trip', () => {
     const s = fresh();
     const id = tableId(s, 'Umsatz');
@@ -2397,6 +2408,27 @@ describe('formula "point mode" (click/drag a cell to insert a reference)', () =>
     expect(ed.text).toBe('=B2');
   });
 
+  it('pointRect outlines the picked cell/range until typing or closing the editor', () => {
+    const s = fresh();
+    const id = s.addTable(s.doc.activeSheetId);
+    const ed = mockEditor(id, '=');
+    s.registerFormulaEditor(ed.handle);
+    expect(s.pointRect.value).toBeNull();
+    s.pointClick(id, 1, 2);
+    expect(s.pointRect.value).toEqual({ tableId: id, c0: 1, r0: 2, c1: 1, r1: 2 });
+    s.pointDrag(id, 2, 3, 0, 1); // dragged up-left: normalised
+    expect(s.pointRect.value).toEqual({ tableId: id, c0: 0, r0: 1, c1: 2, r1: 3 });
+    s.noteFormulaTyped();
+    expect(s.pointRect.value).toBeNull();
+    s.pointClick(id, 0, 0);
+    s.registerFormulaEditor(null);
+    expect(s.pointRect.value).toBeNull();
+    // no formula in the buffer -> nothing picked, nothing outlined
+    s.registerFormulaEditor(mockEditor(id, 'text').handle);
+    s.pointClick(id, 0, 0);
+    expect(s.pointRect.value).toBeNull();
+  });
+
   it('typing between two clicks makes the second an insert, not a replace', () => {
     const s = fresh();
     const id = s.addTable(s.doc.activeSheetId);
@@ -3016,3 +3048,69 @@ describe('whole-column / whole-row references', () => {
     expect(val(s, name, 'A1')).toBe(6);
   });
 });
+
+describe('references of the formula being edited (coloured, draggable)', () => {
+  afterEach(() => useDocument().registerFormulaEditor(null));
+
+  /** Like mockEditor(), but its text is a ref -- as in the real editors,
+   *  which is what keeps store.formulaRefs live. */
+  function reactiveEditor(tableId: string, initialText: string) {
+    const text = ref(initialText);
+    return {
+      handle: {
+        tableId,
+        getState: () => ({ text: text.value, start: text.value.length, end: text.value.length }),
+        replace: (s: number, e: number, value: string) => {
+          text.value = text.value.slice(0, s) + value + text.value.slice(e);
+        },
+      },
+      text,
+    };
+  }
+
+  it('lists each reference with its table, rectangle and colour, following the text', () => {
+    const s = fresh();
+    const id = s.addTable(s.doc.activeSheetId);
+    const other = s.addTable(s.doc.activeSheetId);
+    s.renameObject(other, 'Reisen');
+    const ed = reactiveEditor(id, '=SUMME(B2:C3)+A1+Reisen!A2+B2:C3');
+    s.registerFormulaEditor(ed.handle);
+    const refs = s.formulaRefs.value;
+    expect(refs.map((r) => [r.tableId, r.c0, r.r0, r.c1, r.r1])).toEqual([
+      [id, 1, 1, 2, 2],
+      [id, 0, 0, 0, 0],
+      [other, 0, 1, 0, 1],
+      [id, 1, 1, 2, 2],
+    ]);
+    expect(refs[0].color).not.toBe(refs[1].color);
+    expect(refs[3].color).toBe(refs[0].color); // same reference, same colour
+    ed.text.value = '=D4';
+    expect(s.formulaRefs.value.map((r) => [r.c0, r.r0])).toEqual([[3, 3]]);
+    s.registerFormulaEditor(null);
+    expect(s.formulaRefs.value).toEqual([]);
+  });
+
+  it('whole columns are clamped to the table and marked as not draggable', () => {
+    const s = fresh();
+    const id = s.addTable(s.doc.activeSheetId);
+    s.registerFormulaEditor(reactiveEditor(id, '=SUMME(B:B)').handle);
+    const [r] = s.formulaRefs.value;
+    expect(r).toMatchObject({ c0: 1, r0: 0, c1: 1, r1: s.tableById(id)!.rows - 1, whole: true });
+    expect(s.moveFormulaRef(0, 2, 0, 2, 3)).toBe(false);
+  });
+
+  it('moveFormulaRef rewrites one reference, keeping qualifier and $ locks', () => {
+    const s = fresh();
+    const id = s.addTable(s.doc.activeSheetId);
+    const other = s.addTable(s.doc.activeSheetId);
+    s.renameObject(other, 'Reisen');
+    const ed = reactiveEditor(id, '=SUMME($A$1:B2)*Reisen!C3');
+    s.registerFormulaEditor(ed.handle);
+    s.moveFormulaRef(0, 1, 1, 2, 3); // moved/resized
+    expect(ed.text.value).toBe('=SUMME($B$2:C4)*Reisen!C3');
+    s.moveFormulaRef(1, 0, 0, 1, 1); // a single cell grown into a range
+    expect(ed.text.value).toBe('=SUMME($B$2:C4)*Reisen!A1:B2');
+    s.moveFormulaRef(0, 3, 3, 3, 3); // shrunk to one cell
+    expect(ed.text.value).toBe('=SUMME($D$4)*Reisen!A1:B2');
+  });
+});
diff --git a/app/frontend/store/__tests__/format.spec.ts b/app/frontend/store/__tests__/format.spec.ts
index ebae8ab..e5bb6ef 100644
--- a/app/frontend/store/__tests__/format.spec.ts
+++ b/app/frontend/store/__tests__/format.spec.ts
@@ -1,6 +1,6 @@
 import { describe, it, expect } from 'vitest';
 import { dateToSerial, timeSerial } from '../../engine';
-import { formatValue } from '../format';
+import { formatValue, readableTextOn } from '../format';
 
 describe('formatValue: date/time', () => {
   const day = dateToSerial(2026, 9, 2); // a Wednesday
@@ -46,3 +46,23 @@ describe('formatValue: date/time', () => {
     expect(formatValue(day, 'plain', 'dateiso')).toBe('2026-09-02');
   });
 });
+
+describe('readableTextOn', () => {
+  it('light text on dark fills, dark text on light fills', () => {
+    expect(readableTextOn('#000000')).toBe('#f5f5f7');
+    expect(readableTextOn('#000')).toBe('#f5f5f7');
+    expect(readableTextOn('#1b1b1b')).toBe('#f5f5f7');
+    expect(readableTextOn('#0057ff')).toBe('#f5f5f7');
+    expect(readableTextOn('#ffffff')).toBe('#1d1d1f');
+    expect(readableTextOn('#ffd400')).toBe('#1d1d1f');
+    expect(readableTextOn('#FFF')).toBe('#1d1d1f');
+  });
+
+  it('ignores what it cannot read, and mostly transparent fills', () => {
+    expect(readableTextOn(undefined)).toBeNull();
+    expect(readableTextOn('red')).toBeNull();
+    expect(readableTextOn('#12345')).toBeNull();
+    expect(readableTextOn('#00000020')).toBeNull();
+    expect(readableTextOn('#000000cc')).toBe('#f5f5f7');
+  });
+});
diff --git a/app/frontend/store/document.ts b/app/frontend/store/document.ts
index b672afe..1d7cdeb 100644
--- a/app/frontend/store/document.ts
+++ b/app/frontend/store/document.ts
@@ -27,6 +27,7 @@ import {
   parseA1,
   wholeLineAt,
   formatLinePart,
+  formulaRefSpans,
   parseFormula,
   parseFunctionBlock,
   parseMacroBlock,
@@ -206,6 +207,25 @@ interface ClipboardData {
  * the table the edited cell itself lives in (the "home" table for deciding
  * whether an inserted reference needs a `Name!` qualifier).
  */
+/** Colours for the references of the formula being edited, in text order
+ *  (cycling), same idea as Excel: the n-th reference in the text and its
+ *  outline in the grid share a colour. */
+const REF_COLORS = ['#2f6fde', '#d6453d', '#8e44ad', '#1e9e5a', '#c77c02', '#0b9bb5', '#d6338a'];
+
+/** One reference of the formula being edited, as the grid outlines it. */
+export interface FormulaRefHighlight {
+  /** position among the formula's references -- what `moveFormulaRef` takes */
+  index: number;
+  tableId: string;
+  c0: number;
+  r0: number;
+  c1: number;
+  r1: number;
+  color: string;
+  /** whole column/row: outlined, but not draggable */
+  whole: boolean;
+}
+
 interface FormulaEditorHandle {
   tableId: string;
   getState(): { text: string; start: number; end: number };
@@ -670,6 +690,12 @@ function createStore() {
    *  until the user types something (a plain assignment, not a ref(), so it
    *  never itself triggers reactivity/undo history). */
   let pointSpan: { start: number; end: number } | null = null;
+  /** The cell/range the last point-mode click, drag or arrow key picked, so
+   *  the grid can outline it while it is still the reference being chosen
+   *  (otherwise picking with the keyboard happens completely blind). Lives
+   *  exactly as long as `pointSpan`: typing, a caret click or closing the
+   *  editor ends it. View state only, never synced or saved. */
+  const pointRect = ref<{ tableId: string; c0: number; r0: number; c1: number; r1: number } | null>(null);
   const clampZoom = (z: number) => Math.min(2, Math.max(0.4, Math.round(z * 20) / 20));
 
   function syncWorkbook() {
@@ -2335,7 +2361,7 @@ function createStore() {
     markDirty();
   }
 
-  // ---- cell formatting (alignment, number format, colours, bold/italic) ---
+  // ---- cell formatting (alignment, number format, colours, bold/italic/underline) ---
   const fmtKey = (c: number, r: number) => `${c},${r}`;
   function cellFormat(tableId: string, col: number, row: number): CellFormat {
     return tableById(tableId)?.formats?.[fmtKey(col, row)] ?? {};
@@ -2719,6 +2745,7 @@ function createStore() {
   function registerFormulaEditor(handle: FormulaEditorHandle | null) {
     formulaEditor.value = handle;
     pointSpan = null;
+    pointRect.value = null;
   }
   /** The user typed (as opposed to a click inserting a reference for them):
    *  the next click should insert a fresh reference, not replace the last
@@ -2728,6 +2755,7 @@ function createStore() {
    *  and before picking the next). */
   function noteFormulaTyped() {
     pointSpan = null;
+    pointRect.value = null;
   }
   /** True while the registered editor's buffer is a formula -- point mode
    *  (click-to-insert-reference) only applies then. */
@@ -2893,21 +2921,97 @@ function createStore() {
     pointSpan = { start: span.start, end: span.start + text.length };
     return true;
   }
+  /** The table a reference in the edited formula points at: its own table
+   *  when unqualified, else by name -- preferring the editor's sheet when the
+   *  name exists on several, as the engine does (Workbook.resolveTableName). */
+  function refTableId(homeTableId: string, qualifier: string | null, sheetQualifier?: string): string | null {
+    if (qualifier === null) return homeTableId;
+    const needle = qualifier.trim().toLowerCase();
+    const sheetNeedle = sheetQualifier?.trim().toLowerCase();
+    const candidates = allTables(doc).filter((t) => {
+      if (t.name.trim().toLowerCase() !== needle) return false;
+      if (sheetNeedle === undefined) return true;
+      const sid = sheetIdOfObject(t.id);
+      return (sid && sheetById(sid)?.name.trim().toLowerCase()) === sheetNeedle;
+    });
+    if (candidates.length <= 1) return candidates[0]?.id ?? null;
+    const homeSheet = sheetIdOfObject(homeTableId);
+    return (candidates.find((t) => sheetIdOfObject(t.id) === homeSheet) ?? candidates[0]).id;
+  }
+  /** Every cell/range reference of the formula being edited (in-cell editor
+   *  or formula bar), resolved to its table and clamped to it, so each grid
+   *  can outline the ones that point into it. Reactive on the editor's text:
+   *  both editors' `getState()` read their own text ref. */
+  const formulaRefs = computed<FormulaRefHighlight[]>(() => {
+    const ed = formulaEditor.value;
+    if (!ed) return [];
+    const colorOf = new Map<string, string>();
+    const out: FormulaRefHighlight[] = [];
+    formulaRefSpans(ed.getState().text).forEach((span, index) => {
+      const tableId = refTableId(ed.tableId, span.qualifier, span.sheetQualifier);
+      const t = tableId ? tableById(tableId) : undefined;
+      if (!t) return;
+      const c0 = Math.min(span.a.col, span.b.col);
+      const r0 = Math.min(span.a.row, span.b.row);
+      if (c0 >= t.cols || r0 >= t.rows) return; // entirely outside the table
+      const rect = {
+        c0,
+        r0,
+        c1: Math.min(Math.max(span.a.col, span.b.col), t.cols - 1),
+        r1: Math.min(Math.max(span.a.row, span.b.row), t.rows - 1),
+      };
+      // the same reference written twice keeps one colour (as in Excel)
+      const key = `${t.id}|${rect.c0},${rect.r0},${rect.c1},${rect.r1}`;
+      if (!colorOf.has(key)) colorOf.set(key, REF_COLORS[colorOf.size % REF_COLORS.length]);
+      out.push({ index, tableId: t.id, ...rect, color: colorOf.get(key)!, whole: !!span.whole });
+    });
+    return out;
+  });
+  /** Rewrite the `index`-th reference of the formula being edited to cover
+   *  (c0,r0)-(c1,r1) instead -- dragging a reference outline's edge (move)
+   *  or corner (resize) in the grid, Excel-style. Its qualifier and `$`
+   *  locks stay as written; a range shrunk to one cell becomes a plain cell
+   *  reference. Whole-column/-row references are left alone. */
+  function moveFormulaRef(index: number, c0: number, r0: number, c1: number, r1: number): boolean {
+    const ed = formulaEditor.value;
+    if (!ed) return false;
+    const text = ed.getState().text;
+    const span = formulaRefSpans(text)[index];
+    if (!span || span.whole) return false;
+    const single = span.a.col === span.b.col && span.a.row === span.b.row;
+    const lockB = single ? span.a : span.b;
+    const lo = toA1(Math.min(c0, c1), Math.min(r0, r1), span.a.colAbs, span.a.rowAbs);
+    const hi = toA1(Math.max(c0, c1), Math.max(r0, r1), lockB.colAbs, lockB.rowAbs);
+    const body = c0 === c1 && r0 === r1 ? lo : `${lo}:${hi}`;
+    const next = text.slice(span.start, span.refStart) + body;
+    if (next === text.slice(span.start, span.end)) return true;
+    ed.replace(span.start, span.end, next);
+    // the text around the caret moved: a following grid click must insert a
+    // fresh reference, not overwrite a span that no longer exists
+    pointSpan = null;
+    pointRect.value = null;
+    return true;
+  }
   /** A plain click on (tableId, col, row) while editing a formula: insert or
    *  (immediately after another click/drag, before any typing) replace a
    *  reference at the caret. Returns false when there's no formula editor
    *  active, so the caller can fall back to its normal click handling. */
   function pointClick(tableId: string, col: number, row: number): boolean {
-    return applyPointRef(tableId, toA1(col, row));
+    if (!applyPointRef(tableId, toA1(col, row))) return false;
+    pointRect.value = { tableId, c0: col, r0: row, c1: col, r1: row };
+    return true;
   }
   /** A drag from (c0,r0) to (c1,r1) on tableId while editing a formula:
    *  insert/replace a *range* reference, meant to be called live as the drag
    *  updates (each call replaces the same span, growing/shrinking the range
    *  as the user drags), not just once at the end. */
   function pointDrag(tableId: string, c0: number, r0: number, c1: number, r1: number): boolean {
-    const a = toA1(Math.min(c0, c1), Math.min(r0, r1));
-    const b = toA1(Math.max(c0, c1), Math.max(r0, r1));
-    return applyPointRef(tableId, a === b ? a : `${a}:${b}`);
+    const rect = { tableId, c0: Math.min(c0, c1), r0: Math.min(r0, r1), c1: Math.max(c0, c1), r1: Math.max(r0, r1) };
+    const a = toA1(rect.c0, rect.r0);
+    const b = toA1(rect.c1, rect.r1);
+    if (!applyPointRef(tableId, a === b ? a : `${a}:${b}`)) return false;
+    pointRect.value = rect;
+    return true;
   }
 
   // The "active cell" is always the anchor -- the first cell of the current
@@ -3224,6 +3328,9 @@ function createStore() {
     jumpToNameInput,
     pointClick,
     pointDrag,
+    pointRect,
+    formulaRefs,
+    moveFormulaRef,
     // document
     replaceDocument,
     newDocument,
diff --git a/app/frontend/store/format.ts b/app/frontend/store/format.ts
index 7b82df4..322f36e 100644
--- a/app/frontend/store/format.ts
+++ b/app/frontend/store/format.ts
@@ -165,3 +165,35 @@ export function rawString(v: CellValue): string {
 export function isNumeric(v: CellValue): boolean {
   return typeof v === 'number' && Number.isFinite(v);
 }
+
+// ---- readable text on a fill ---------------------------------------------
+
+const DARK_TEXT = '#1d1d1f';
+const LIGHT_TEXT = '#f5f5f7';
+
+/** sRGB channel (0–255) → linear light, per WCAG 2.x */
+const linear = (c: number) => {
+  const s = c / 255;
+  return s <= 0.03928 ? s / 12.92 : ((s + 0.055) / 1.055) ** 2.4;
+};
+
+/**
+ * Text colour that stays readable on the fill `bg` (#rgb, #rgba, #rrggbb,
+ * #rrggbbaa): dark or light, whichever contrasts more (WCAG luminance).
+ * Used when a cell or table has a fill but no text colour of its own -- the
+ * theme's text colour would otherwise land on it regardless (black text on
+ * a black fill). `null` when `bg` can't be read or is mostly transparent
+ * (the theme's surface shows through, its text colour already fits).
+ */
+export function readableTextOn(bg: string | undefined | null): string | null {
+  const m = /^#([0-9a-f]{3,4}|[0-9a-f]{6}|[0-9a-f]{8})$/i.exec((bg ?? '').trim());
+  if (!m) return null;
+  let hex = m[1];
+  if (hex.length <= 4) hex = [...hex].map((ch) => ch + ch).join('');
+  const [r, g, b] = [0, 2, 4].map((i) => parseInt(hex.slice(i, i + 2), 16));
+  const alpha = hex.length === 8 ? parseInt(hex.slice(6, 8), 16) / 255 : 1;
+  if (alpha < 0.5) return null;
+  const lum = 0.2126 * linear(r) + 0.7152 * linear(g) + 0.0722 * linear(b);
+  // contrast with black vs. with white: (L + 0.05) / 0.05 vs 1.05 / (L + 0.05)
+  return (lum + 0.05) / 0.05 >= 1.05 / (lum + 0.05) ? DARK_TEXT : LIGHT_TEXT;
+}
diff --git a/app/frontend/store/types.ts b/app/frontend/store/types.ts
index 3fc7fef..fb4bc96 100644
--- a/app/frontend/store/types.ts
+++ b/app/frontend/store/types.ts
@@ -42,6 +42,7 @@ export interface CellFormat {
   bg?: string;
   bold?: boolean;
   italic?: boolean;
+  underline?: boolean;
 }
 
 /** How a table object is sized on the canvas. */