diff --git a/app/client/lib/TokenField.ts b/app/client/lib/TokenField.ts
new file mode 100644
index 00000000..25761798
--- /dev/null
+++ b/app/client/lib/TokenField.ts
@@ -0,0 +1,608 @@
+/**
+ * A full-featured implementation of tokenfield (aka "pillbox", "tag list", etc).
+ *
+ * Supported features:
+ * - Each token includes an "x" button to delete it.
+ * - Click on a token to select;
+ *   Shift+click to extend selection;
+ *   Ctrl+click for non-contigous selection.
+ * - Arrow keys to move selection.
+ *   Shift + arrow keys to extend selection.
+ * - Cmd+A to select all options.
+ * - Delete/Backspace delete selection. If no selection, Backspace deletes the last item.
+ * - Copy-cut is supported for a selection. By default CSV-encodes token labels.
+ * - Paste is supported into input textbox, or to replace a selection.
+ * - Tokens or a selection of tokens may be dragged to move within the tokenfield.
+ * - Supports undo/redo for token changes.
+ */
+import { ACItem } from 'app/client/lib/ACIndex';
+import { modKeyProp } from 'app/client/lib/browserInfo';
+import { Autocomplete, IAutocompleteOptions } from 'app/client/lib/autocomplete';
+import { colors, testId } from 'app/client/ui2018/cssVars';
+import { icon } from 'app/client/ui2018/icons';
+import { csvDecodeRow, csvEncodeRow } from 'app/common/csvFormat';
+import { computedArray, IObsArraySplice, ObsArray, obsArray, Observable } from 'grainjs';
+import { Disposable, dom, DomContents, Holder, styled } from 'grainjs';
+
+export interface IToken {
+  label: string;
+}
+
+export interface ITokenFieldOptions {
+  initialValue: IToken[];
+  renderToken: (token: IToken) => DomContents;
+  createToken: (inputText: string) => IToken|undefined;
+  acOptions?: IAutocompleteOptions<IToken & ACItem>;
+  openAutocompleteOnFocus?: boolean;
+
+  // Allows overriding how tokens are copied to the clipboard, or retrieved from it.
+  // By default, tokens are placed into clipboard as text/plain comma-separated token labels, with
+  // CSV escaping, and pasted from clipboard by applying createToken() to parsed CSV text.
+  tokensToClipboard?: (tokens: IToken[], clipboard: DataTransfer) => void;
+  clipboardToTokens?: (clipboard: DataTransfer) => IToken[];
+}
+
+// TokenWrap serves to distinguish multiple instances of the same token in the list.
+class TokenWrap {
+  constructor(public token: IToken) {}
+}
+
+class UndoItem {
+  constructor(public redo: () => void, public undo: () => void) {}
+}
+
+export class TokenField extends Disposable {
+  public tokensObs: ObsArray<IToken>;
+
+  private _acHolder = Holder.create<Autocomplete<IToken & ACItem>>(this);
+  private _acOptions: IAutocompleteOptions<IToken & ACItem>|undefined;
+  private _rootElem: HTMLElement;
+  private _textInput: HTMLInputElement;
+
+  // ClipboardAPI events work as expected only when the focus is in an actual input.
+  // This is where we place focus when we have some tokens selected.
+  private _hiddenInput: HTMLInputElement;
+
+  // Keys to navigate tokens. In a vertical list, these would be changed to Up/Down.
+  // TODO Support a vertical list.
+  private _keyPrev = 'ArrowLeft';
+  private _keyNext = 'ArrowRight';
+
+  private _tokens = this.autoDispose(obsArray<TokenWrap>());
+  private _selection = Observable.create(this, new Set<TokenWrap>());
+  private _selectionAnchor: TokenWrap|null = null;
+  private _undoStack: UndoItem[] = [];
+  private _undoIndex = 0;   // The last action done; next to undo.
+  private _inUndoRedo = false;
+
+  constructor(private _options: ITokenFieldOptions) {
+    super();
+    const addSelectedItem = this._addSelectedItem.bind(this);
+    const openAutocomplete = this._openAutocomplete.bind(this);
+    this._acOptions = _options.acOptions && {..._options.acOptions, onClick: addSelectedItem};
+    this._tokens.set(_options.initialValue.map(t => new TokenWrap(t)));
+    this.tokensObs = this.autoDispose(computedArray(this._tokens, t => t.token));
+
+    // We can capture undo info in a consistent way as long as we change _tokens using its
+    // obsArray interface, by listening to the splice events.
+    this.autoDispose(this._tokens.addListener(this._recordUndo.bind(this)));
+
+    this._rootElem = cssTokenField(
+      {tabIndex: '-1'},
+      dom.forEach(this._tokens, (t) =>
+        cssToken(this._options.renderToken(t.token),
+          cssDeleteIcon('CrossSmall', testId('tokenfield-delete')),
+          dom.cls('selected', (use) => use(this._selection).has(t)),
+          dom.on('click', (ev) => this._onTokenClick(ev, t)),
+          dom.on('mousedown', (ev) => this._onMouseDown(ev, t)),
+          testId('tokenfield-token')
+        ),
+      ),
+      cssInputWrapper(
+        this._textInput = cssTokenInput(
+          dom.on('focus', this._onInputFocus.bind(this)),
+          dom.on('blur', () => { this._acHolder.clear(); }),
+          dom.onKeyDown({
+            Escape: () => { this._acHolder.clear(); },
+            Enter: addSelectedItem,
+            ArrowDown$: openAutocomplete,
+            Tab$: (ev) => {
+              // Only treat tab specially if there is some token-adding in progress.
+              if (this._textInput.value !== '' || !this._acHolder.isEmpty()) {
+                ev.stopPropagation();
+                ev.preventDefault();
+                addSelectedItem();
+              }
+            },
+          }),
+          dom.on('input', openAutocomplete),
+          testId('tokenfield-input'),
+        ),
+      ),
+      dom.onKeyDown({
+        a$: this._maybeSelectAllTokens.bind(this),
+        Backspace$: this._maybeBackspace.bind(this),
+        Delete$: this._maybeDelete.bind(this),
+        [this._keyPrev + '$']: (ev) => this._maybeAdvance(ev, -1),
+        [this._keyNext + '$']: (ev) => this._maybeAdvance(ev, +1),
+        // ['Mod+z'] triggers undo; ['Mod+Shift+Z', 'Ctrl+y' ] trigger redo
+        z$: (ev) => { if (ev[modKeyProp()]) { ev.shiftKey ? this._redo(ev) : this._undo(ev); } },
+        y$: (ev) => { if (ev.ctrlKey && !ev.shiftKey) { this._redo(ev); } },
+      }),
+      this._hiddenInput = cssHiddenInput({type: 'text', tabIndex: '-1'},
+        dom.on('blur', (ev) => {
+          if (ev.relatedTarget && ev.relatedTarget !== this._rootElem) {
+            this._selectionAnchor = null;
+            this._selection.set(new Set());
+          }
+        }),
+      ),
+      dom.on('focus', () => this._hiddenInput.focus()),
+      dom.on('copy', this._onCopyEvent.bind(this)),
+      dom.on('cut', this._onCutEvent.bind(this)),
+      dom.on('paste', this._onPasteEvent.bind(this)),
+      testId('tokenfield'),
+    );
+  }
+
+  public attach(elem: HTMLElement): void {
+    elem.appendChild(this._rootElem);
+  }
+
+  // Open the autocomplete dropdown, if autocomplete was configured in the options.
+  private _openAutocomplete() {
+    if (this._acOptions && this._acHolder.isEmpty()) {
+      Autocomplete.create(this._acHolder, this._textInput, this._acOptions);
+    }
+  }
+
+  // Adds the typed-in or selected item. If an item is selected in autocomplete dropdown, adds
+  // that; otherwise if options.createToken is present, creates a token from text input value.
+  private _addSelectedItem() {
+    let item: IToken|undefined = this._acHolder.get()?.getSelectedItem();
+    if (!item && this._options.createToken && this._textInput.value) {
+      item = this._options.createToken(this._textInput.value);
+    }
+    if (item) {
+      this._tokens.push(new TokenWrap(item));
+      this._textInput.value = '';
+      this._acHolder.clear();
+    }
+  }
+
+  // Handler for when text input is focused: clears selection, optionally opens dropdown.
+  private _onInputFocus() {
+    this._selectionAnchor = null;
+    this._selection.set(new Set());
+    if (this._options.openAutocompleteOnFocus) {
+      this._openAutocomplete();
+    }
+  }
+
+  // Handle for a click on a token or the token's delete button. This handles selection, including
+  // Shift+Click and Ctrl+Click.
+  private _onTokenClick(ev: MouseEvent, t: TokenWrap) {
+    const idx = this._tokens.get().indexOf(t);
+    if (idx < 0) { return; }
+    if (ev.target && (ev.target as HTMLElement).matches('.' + cssDeleteIcon.className)) {
+      // Delete token.
+      this._tokens.splice(idx, 1);
+    } else {
+      const fromIdx = this._selectionAnchor ? this._tokens.get().indexOf(this._selectionAnchor) : -1;
+      if (ev.shiftKey && fromIdx >= 0) {
+        // Shift+Click selects range from selectionAnchor to the clicked token.
+        const [first, last] = fromIdx <= idx ? [fromIdx, idx] : [idx, fromIdx];
+        this._selection.set(new Set(this._tokens.get().slice(first, last + 1)));
+      } else if (ev[modKeyProp()] && fromIdx >= 0) {
+        // Ctrl+Click (or Command+Click on mac) toggles the clicked token.
+        this._toggleTokenSelection(t);
+      } else {
+        // Plain click, or any click in the absence of an anchor element, sets the anchor and
+        // selects just this element.
+        this._resetTokenSelection(t);
+      }
+    }
+    this._setFocus();
+  }
+
+  private _maybeSelectAllTokens(ev: KeyboardEvent) {
+    if (ev[modKeyProp()] && this._textInput.value === '') {
+      ev.stopPropagation();
+      ev.preventDefault();
+      const tokens = this._tokens.get();
+      this._selection.set(new Set(tokens));
+      this._selectionAnchor = tokens ? tokens[0] : null;
+      this._setFocus();
+    }
+  }
+
+  // Set focus appropriately to the textInput or to the outer container.
+  private _setFocus() {
+    if (this._selection.get().size === 0) {
+      this._textInput.focus();
+    } else {
+      this._hiddenInput.focus();
+    }
+  }
+
+  private _maybeBackspace(ev: KeyboardEvent) {
+    if (this._textInput.value === '') {
+      ev.stopPropagation();
+      ev.preventDefault();
+      if (this._selection.get().size === 0) {
+        this._tokens.pop();
+      } else {
+        this._deleteTokens(this._selection.get(), -1);
+      }
+    }
+  }
+
+  private _maybeDelete(ev: KeyboardEvent) {
+    if (this._textInput.value === '' && this._selection.get().size > 0) {
+      ev.stopPropagation();
+      ev.preventDefault();
+      this._deleteTokens(this._selection.get(), 1);
+    }
+  }
+
+  // Handle arrow and shift+arrow keys, when the text input is empty.
+  private _maybeAdvance(ev: KeyboardEvent, advance: 1|-1): void {
+    if (this._textInput.value !== '') {
+      return;
+    }
+    const tokens = this._tokens.get();
+    const anchorIdx = this._selectionAnchor ? tokens.indexOf(this._selectionAnchor) : -1;
+
+    if (ev.shiftKey && this._selection.get().size > 0 && anchorIdx >= 0) {
+      // For shift+arrows, we either extend or reduce the selection, depending on whether we are
+      // walking away from the anchor or back towards it.
+      const [first, last] = this._getSelectedIndexRange(this._selection.get());
+      if (last < 0) { return; }
+      const toggleIdx = (advance > 0) ?
+        (last === anchorIdx && first < anchorIdx ? first : last + 1) :
+        (first === anchorIdx && last > anchorIdx ? last : first - 1);
+      const t = tokens[toggleIdx];
+      if (t) {
+        ev.stopPropagation();
+        ev.preventDefault();
+        this._toggleTokenSelection(t);
+        this._setFocus();
+      }
+    } else {
+      // For arrow keys, move to the next token after the selection.
+      let next: TokenWrap|null = null;
+      if (this._selection.get().size > 0) {
+        next = this._getNextToken(this._selection.get(), advance);
+      } else if (advance < 0 && tokens.length > 0) {
+        next = tokens[tokens.length - 1];
+      }
+      // If no next token and we are moving to the right, we should end up back in the text input.
+      if (next || advance > 0) {
+        ev.stopPropagation();
+        ev.preventDefault();
+        this._resetTokenSelection(next);
+        this._setFocus();
+      }
+    }
+  }
+
+  private _toggleTokenSelection(token: TokenWrap) {
+    const selection = this._selection.get();
+    if (selection.has(token)) {
+      selection.delete(token);
+    } else {
+      selection.add(token);
+    }
+    // We use .setAndTrigger() to set a value that's identical (by reference) to the previous one.
+    this._selection.setAndTrigger(selection);
+  }
+
+  private _resetTokenSelection(token: TokenWrap|null) {
+    this._selectionAnchor = token;
+    this._selection.set(token ? new Set([token]) : new Set());
+  }
+
+  // Delete the given set of tokens, and select either the following or the preceding one.
+  private _deleteTokens(toDelete: Set<TokenWrap>, advance: 1|-1|0) {
+    if (this._selection.get().size === 0) { return; }
+    const selectAfter = advance ? this._getNextToken(toDelete, advance) : null;
+    this._tokens.set(this._tokens.get().filter(t => !toDelete.has(t)));
+    this._resetTokenSelection(selectAfter);
+    this._setFocus();
+  }
+
+  private _getNextToken(selection: Set<TokenWrap>, advance: 1|-1): TokenWrap|null {
+    const [first, last] = this._getSelectedIndexRange(selection);
+    if (last < 0) { return null; }
+    return this._tokens.get()[advance > 0 ? last + 1 : first - 1] || null;
+  }
+
+  private _getSelectedIndexRange(selection: Set<TokenWrap>): [number, number] {
+    const tokens = this._tokens.get();
+    let first = -1, last = -1;
+    for (let i = 0; i < tokens.length; i++) {
+      if (selection.has(tokens[i])) {
+        if (first === -1) { first = i; }
+        last = i;
+      }
+    }
+    return [first, last];
+  }
+
+  private _onCopyEvent(ev: ClipboardEvent): boolean {
+    if (!ev.clipboardData || !this._selection.get().size) { return false; }
+    ev.preventDefault();  // Required for overriding: https://www.w3.org/TR/clipboard-apis/#override-copy
+
+    const selected = this._selection.get();
+    const tokens = this._tokens.get().filter(t => selected.has(t));
+    if (this._options.tokensToClipboard) {
+      this._options.tokensToClipboard(tokens.map(t => t.token), ev.clipboardData);
+    } else {
+      const values = tokens.map(t => t.token.label);
+      ev.clipboardData.setData('text/plain', csvEncodeRow(values, {prettier: true}));
+    }
+    return true;
+  }
+
+  private _onCutEvent(ev: ClipboardEvent) {
+    if (this._onCopyEvent(ev)) {
+      this._deleteTokens(this._selection.get(), 0);
+    }
+  }
+
+  private _onPasteEvent(ev: ClipboardEvent) {
+    if (!ev.clipboardData) { return; }
+    ev.preventDefault();
+    let tokens: IToken[];
+    if (this._options.clipboardToTokens) {
+      tokens = this._options.clipboardToTokens(ev.clipboardData);
+    } else {
+      const text = ev.clipboardData.getData('text/plain');
+      const values = csvDecodeRow(text);
+      tokens = values.map(v => this._options.createToken(v)).filter((t): t is IToken => Boolean(t));
+    }
+    if (!tokens.length) { return; }
+    const wrappedTokens = tokens.map(t => new TokenWrap(t));
+    this._combineUndo(() => {
+      this._deleteTokens(this._selection.get(), 1);
+      const anchorIdx = this._selectionAnchor ? this._tokens.get().indexOf(this._selectionAnchor) : -1;
+      if (anchorIdx >= 0) {
+        this._tokens.splice(anchorIdx, 0, ...wrappedTokens);
+        this._selectionAnchor = wrappedTokens[0];
+        this._selection.set(new Set(wrappedTokens));
+      } else {
+        this._tokens.push(...wrappedTokens);
+        this._resetTokenSelection(null);
+      }
+    });
+    this._setFocus();
+  }
+
+  // For a mousedown on a token, register events for mousemove/mouseup, and start dragging as soon
+  // as mousemove occurs.
+  private _onMouseDown(startEvent: MouseEvent, t: TokenWrap) {
+    const xInitial = startEvent.clientX;
+    const yInitial = startEvent.clientY;
+    const dragTargetSelector = `.${cssToken.className}, .${cssInputWrapper.className}`;
+
+    let started = false;
+    let allTargets: HTMLElement[];
+    let tokenList: HTMLElement[];
+
+    const onMove = (ev: MouseEvent) => {
+      if (!started) {
+        started = true;
+        // If we started dragging an element that's not part of the selection, reset the selection
+        // to just that element. After this, we are always dragging the active selection.
+        if (!this._selection.get().has(t)) {
+          this._resetTokenSelection(t);
+        }
+
+        this._rootElem.classList.add('token-dragactive');
+
+        // Get a list of all drag targets, and add a CSS class that shows drop location on hover.
+        allTargets = Array.prototype.filter.call(this._rootElem.children, el => el.matches(dragTargetSelector));
+        allTargets.forEach(el => el.classList.add(cssDragTarget.className));
+
+        // Get a list of element we are dragging, and add a CSS class to show them as dragged.
+        tokenList = allTargets.filter(el => el.matches('.selected'));
+        tokenList.forEach(el => el.classList.add('token-dragging'));
+      }
+      const xOffset = ev.clientX - xInitial;
+      const yOffset = ev.clientY - yInitial;
+      const transform = `translate(${xOffset}px, ${yOffset}px)`;
+      tokenList.forEach(el => { el.style.transform = transform; });
+    };
+
+    const onStop = (ev: MouseEvent) => {
+      moveLis.dispose();
+      stopLis.dispose();
+
+      // Stop here if dragging never started.
+      if (!started) { return; }
+
+      // Restore all style changes.
+      this._rootElem.classList.remove('token-dragactive');
+      allTargets.forEach(el => el.classList.remove(cssDragTarget.className));
+      tokenList.forEach(el => el.classList.remove('token-dragging'));
+      tokenList.forEach(el => { el.style.transform = ''; });
+
+      // Find the token before which we are inserting the dragged elements. If inserting at the
+      // end (just before or over the input box), destToken will be undefined.
+      const index = allTargets.indexOf(ev.target as HTMLElement);
+      if (index < 0) { return; }
+      const destToken: TokenWrap|undefined = this._tokens.get()[index];
+
+      const selection = this._selection.get();
+      if (selection.has(destToken)) { return; }   // Not actually moving anywhere new.
+
+      const movedTokens = this._tokens.get().filter(tok => selection.has(tok));
+      if (!movedTokens.length) { return; }        // Didn't find any tokens to move.
+
+      this._combineUndo(() => {
+        this._deleteTokens(selection, 0);
+        // Find destination again after the deletion (it's likely to have changed).
+        const destIndex = destToken ? this._tokens.get().indexOf(destToken) : this._tokens.get().length;
+        // Move the tokens and mark them as selected.
+        this._tokens.splice(destIndex, 0, ...movedTokens);
+        this._selectionAnchor = movedTokens[0];
+        this._selection.set(new Set(movedTokens));
+      });
+    };
+
+    const moveLis = dom.onElem(document, 'mousemove', onMove, {useCapture: true});
+    const stopLis = dom.onElem(document, 'mouseup', onStop, {useCapture: true});
+  }
+
+  private _recordUndo(val: TokenWrap[], prev: TokenWrap[], change?: IObsArraySplice<TokenWrap>) {
+    if (this._inUndoRedo) { return; }
+    const splice = change || {start: 0, numAdded: val.length, deleted: [...prev]};
+    const newTokens = val.slice(splice.start, splice.start + splice.numAdded);
+    const redo = () => this._tokens.splice(splice.start, splice.deleted.length, ...newTokens);
+    const undo = () => this._tokens.splice(splice.start, splice.numAdded, ...splice.deleted);
+    this._undoIndex = Math.min(this._undoIndex + 1, this._undoStack.length);
+    this._undoStack.splice(this._undoIndex, this._undoStack.length, new UndoItem(redo, undo));
+  }
+
+  private _combineUndo(callback: () => void) {
+    const nextAction = this._undoIndex + 1;
+    try {
+      callback();
+    } finally {
+      if (this._undoStack.length > nextAction + 1) {
+        // If multiple actions were added, combine them into one.
+        const actions = this._undoStack.slice(nextAction);
+        const redo = () => actions.forEach(a => a.redo());
+        const undo = () => actions.slice().reverse().forEach(a => a.undo());
+        this._undoIndex = nextAction;
+        this._undoStack.splice(this._undoIndex, actions.length, new UndoItem(redo, undo));
+      }
+    }
+  }
+
+  private _undo(ev: KeyboardEvent): void {
+    if (this._textInput.value === '' && this._undoIndex >= 0 && this._undoIndex < this._undoStack.length) {
+      ev.stopPropagation();
+      ev.preventDefault();
+      this._inUndoRedo = true;
+      try {
+        this._undoStack[this._undoIndex].undo();
+        this._undoIndex--;
+      } finally {
+        this._inUndoRedo = false;
+      }
+    }
+  }
+
+  private _redo(ev: KeyboardEvent): void {
+    if (this._undoIndex + 1 < this._undoStack.length) {
+      ev.stopPropagation();
+      ev.preventDefault();
+      this._inUndoRedo = true;
+      try {
+        this._undoIndex += 1;
+        this._undoStack[this._undoIndex].redo();
+      } finally {
+        this._inUndoRedo = false;
+      }
+    }
+  }
+}
+
+const cssTokenField = styled('div', `
+  display: flex;
+  border: 1px solid ${colors.darkGrey};
+  border-radius: 3px;
+  padding: 0 4px;
+
+  &.token-dragactive {
+    cursor: grabbing;
+  }
+`);
+
+const cssToken = styled('div', `
+  position: relative;
+  flex: none;
+  border-radius: 3px;
+  background-color: ${colors.mediumGreyOpaque};
+  padding: 4px;
+  margin: 3px 2px;
+  line-height: 16px;
+  user-select: none;
+  cursor: grab;
+
+  &.selected {
+    background-color: ${colors.darkGrey};
+  }
+  &.token-dragging {
+    pointer-events: none;
+    z-index: 1;
+    opacity: 0.7;
+  }
+  .${cssTokenField.className}.token-dragactive & {
+    cursor: unset;
+  }
+`);
+
+const cssInputWrapper = styled('div', `
+  position: relative;
+  flex: auto;
+  margin: 3px 2px;
+  display: flex;
+`);
+
+const cssTokenInput = styled('input', `
+  flex: auto;
+  -webkit-appearance: none;
+  -moz-appearance: none;
+  padding: 0;
+  border: none;
+  outline: none;
+`);
+
+// This class is applied to tokens and the input box on start of dragging, to use them as drag
+// targets. Insertion point will always be to the left of them. While dragging, these include a
+// transparent pseudo-element to cover some area to the left, to know when it's a suitable drop
+// position. While the drag is over the element (or its extension), it gets shifted to show
+// the user the location of the drop using another pseudo-element.
+const cssDragTarget = styled('div', `
+  &::before {
+    content: "";
+    position: absolute;
+    left: -8px;
+    right: 50%;
+    top: 0px;
+    bottom: 0px;
+  }
+  &:hover {
+    transform: translateX(2px);
+  }
+  &:hover::after {
+    content: "";
+    position: absolute;
+    background-color: ${colors.lightGreen};
+    width: 2px;
+    top: 0px;
+    bottom: 0px;
+    left: -4px;
+  }
+`);
+
+const cssHiddenInput = styled('input', `
+  left: -10000px;
+  width: 1px;
+  position: absolute;
+`);
+
+const cssDeleteIcon = styled(icon, `
+  vertical-align: bottom;
+  margin-left: 4px;
+  cursor: pointer;
+  --icon-color: ${colors.slate};
+  &:hover {
+    --icon-color: ${colors.dark};
+  }
+  .${cssTokenField.className}.token-dragactive & {
+    cursor: unset;
+  }
+`);
diff --git a/app/client/lib/browserInfo.ts b/app/client/lib/browserInfo.ts
index f8672cf8..711068cf 100644
--- a/app/client/lib/browserInfo.ts
+++ b/app/client/lib/browserInfo.ts
@@ -18,3 +18,11 @@ export function isDesktop() {
 export function isIOS() {
   return navigator.platform && /iPad|iPhone|iPod/.test(navigator.platform);
 }
+
+// Returns 'metaKey' on Mac / iOS, and 'ctrlKey' elsewhere. This is useful for various keyboard
+// interactions that use Control on Windows and Linux, and Command key on Mac for the same
+// purpose. Suitable to use with KeyboardEvent and MouseEvent.
+// (Note: Mousetrap.js uses the same logic to interpret its "mod" key alias.)
+export function modKeyProp(): 'metaKey'|'ctrlKey' {
+  return /Mac|iPod|iPhone|iPad/.test(navigator.platform) ? 'metaKey' : 'ctrlKey';
+}
diff --git a/app/client/ui/mouseDrag.ts b/app/client/ui/mouseDrag.ts
index edec1c52..34a39404 100644
--- a/app/client/ui/mouseDrag.ts
+++ b/app/client/ui/mouseDrag.ts
@@ -17,7 +17,7 @@ export interface MouseDragHandler {
   onStop(endEv: MouseEvent): void;
 }
 
-export type MouseDragStart = (startEv: MouseEvent, elem: Element) => MouseDragHandler|null;
+export type MouseDragStart = (startEv: MouseEvent, elem: HTMLElement) => MouseDragHandler|null;
 
 export function mouseDragElem(elem: HTMLElement, onStart: MouseDragStart): IDisposable {
 
@@ -30,7 +30,7 @@ export function mouseDrag(onStart: MouseDragStart): DomElementMethod {
   return (elem) => { mouseDragElem(elem, onStart); };
 }
 
-function _startDragging(startEv: MouseEvent, elem: Element, onStart: MouseDragStart) {
+function _startDragging(startEv: MouseEvent, elem: HTMLElement, onStart: MouseDragStart) {
   const dragHandler = onStart(startEv, elem);
   if (dragHandler) {
 
diff --git a/app/common/csvFormat.ts b/app/common/csvFormat.ts
new file mode 100644
index 00000000..e204dd72
--- /dev/null
+++ b/app/common/csvFormat.ts
@@ -0,0 +1,38 @@
+/**
+ * Simple utilities for escaping/quoting/parsing CSV data.
+ *
+ * This only supports the default Excel-like encoding, in which fields containing any separators
+ * or quotes get quoted (using '"'), and quotes get doubled.
+ *
+ * Quoting is also applied when values contain leading or trailing whitespace, and on parsing,
+ * leading or trailing whitespace in unquoted values is trimmed, so that "," or ", " may be used
+ * as a separator.
+ *
+ * This is intended for copy-pasting multi-choice values, where plain comma-separated text is the
+ * most user-friendly, and CSV encoding is used to ensure we can handle arbitrary values.
+ */
+
+// Encode a row. If {prettier: true} is set, separate output with ", ". Leading whitespace gets
+// encoded in any case.
+export function csvEncodeRow(values: string[], options: {prettier?: boolean} = {}): string {
+  return values.map(csvEncodeCell).join(options.prettier ? ", " : ",");
+}
+
+export function csvDecodeRow(text: string): string[] {
+  // Clever regexp from https://github.com/micnews/csv-line
+  const parts = text.split(/((?:(?:"[^"]*")|[^,])*)/);
+  const main = parts.filter((v, idx) => idx % 2).map(csvDecodeCell);
+  // The "delimiter" (odd-numbered parts) is our content. If it's not at the start/end, it means
+  // we have commas, and should include empty fields at those ends.
+  if (parts[0]) { main.unshift(""); }
+  if (parts[parts.length - 1]) { main.push(""); }
+  return main;
+}
+
+export function csvEncodeCell(value: string): string {
+  return /[,\r\n"]|^\s|\s$/.test(value) ? '"' + value.replace(/"/g, '""') + '"' : value;
+}
+
+export function csvDecodeCell(value: string): string {
+  return value.trim().replace(/^"|"$/g, '').replace(/""/g, '"');
+}
diff --git a/test/nbrowser/gristUtils.ts b/test/nbrowser/gristUtils.ts
index 957d2d41..d3989ffe 100644
--- a/test/nbrowser/gristUtils.ts
+++ b/test/nbrowser/gristUtils.ts
@@ -964,6 +964,10 @@ export async function copyKey() {
   return await isMac() ? Key.chord(Key.CONTROL, Key.INSERT) : Key.chord(Key.CONTROL, 'c');
 }
 
+export async function cutKey() {
+  return await isMac() ? Key.chord(Key.CONTROL, Key.DELETE) : Key.chord(Key.CONTROL, 'x');
+}
+
 export async function pasteKey() {
   return await isMac() ? Key.chord(Key.SHIFT, Key.INSERT) : Key.chord(Key.CONTROL, 'v');
 }