diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7aff3e76..9ff5117f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,24 @@
+## Unreleased
+
+- Screen readers: a tappable frame or shape reads as a button. One with no
+  text inside (an icon button) is named after its node, or its icon when the
+  node keeps a default name like "Frame 3". Nodes no longer offer a long
+  press that does nothing.
+- Show toast action: shows a message near the bottom of the app over every
+  route, with variables and formulas in the text. A new toast replaces the
+  one on screen.
+- Formulas: `${= expression}` in any text, bound property, condition or
+  action value computes a result, e.g. `${= money(qty * price)}`,
+  `${= sum(storage.cart, 'total')}` or `${= count > 1 ? 'drinks' : 'drink'}`.
+  They support arithmetic, comparisons, `&& || !`, `a ? b : c`, lists, and
+  the functions money, fixed, round, floor, ceil, abs, min, max, sum, count,
+  length, if, plural, join, upper, lower, contains, number, text, isEmpty and
+  isNotEmpty. A value that is exactly one formula keeps its type. Nodes
+  rebuild when the variables a formula reads change.
+- Style properties at runtime: `fill`, `stroke`, `opacity`, `width` and
+  `height` follow conditions, variables or formulas bound to them, and set
+  value actions.
+
 ## 7.2.0
 
 - Require codelessly_api 5.2.0.
diff --git a/example/pubspec.yaml b/example/pubspec.yaml
index e0640bdc..dd3aa05b 100644
--- a/example/pubspec.yaml
+++ b/example/pubspec.yaml
@@ -23,3 +23,12 @@ dev_dependencies:
 
 flutter:
   uses-material-design: true
+
+# Temporary: the show toast action needs codelessly_api from
+# Codelessly/CodelesslyAPI#37, merged but not yet published. Remove once
+# codelessly_api is released.
+dependency_overrides:
+  codelessly_api:
+    git:
+      url: https://github.com/Codelessly/CodelesslyAPI.git
+      ref: master
diff --git a/lib/codelessly_sdk.dart b/lib/codelessly_sdk.dart
index 0fb7c904..2d4c9f00 100644
--- a/lib/codelessly_sdk.dart
+++ b/lib/codelessly_sdk.dart
@@ -37,6 +37,7 @@ export 'src/utils/extensions.dart';
 export 'src/utils/flutter_icons_data_map.dart';
 export 'src/utils/flutter_icons_names_map.dart';
 export 'src/utils/font_parser.dart';
+export 'src/utils/formula.dart';
 export 'src/utils/image_builder.dart';
 export 'src/utils/observable.dart';
 export 'src/utils/rgb_to_color.dart';
diff --git a/lib/src/functions/app_toast.dart b/lib/src/functions/app_toast.dart
new file mode 100644
index 00000000..021e2bde
--- /dev/null
+++ b/lib/src/functions/app_toast.dart
@@ -0,0 +1,156 @@
+import 'dart:async';
+
+import 'package:codelessly_api/codelessly_api.dart';
+import 'package:flutter/material.dart';
+
+import '../../codelessly_sdk.dart';
+
+/// Shows [ShowToastAction] messages: a pill near the bottom of the screen
+/// that fades in, stays for the action's duration and fades out. A new toast
+/// replaces the one on screen.
+class AppToast {
+  AppToast._();
+
+  static OverlayEntry? _current;
+
+  /// Shows [action]'s message. Returns false when there is no overlay to
+  /// show it in.
+  static bool show(BuildContext context, ShowToastAction action) {
+    final OverlayState? overlay = Overlay.maybeOf(context, rootOverlay: true);
+    if (overlay == null) return false;
+
+    // Read variables now: the action that follows may navigate away.
+    final String message = PropertyValueDelegate.substituteVariables(
+      action.message,
+      scopedValues: ScopedValues.of(context),
+      nullSubstitutionMode: NullSubstitutionMode.emptyString,
+    );
+
+    hide();
+    late final OverlayEntry entry;
+    entry = OverlayEntry(
+      builder: (context) => _ToastView(
+        action: action,
+        message: message,
+        onDone: () {
+          if (_current == entry) _current = null;
+          if (entry.mounted) entry.remove();
+        },
+      ),
+    );
+    _current = entry;
+    overlay.insert(entry);
+    return true;
+  }
+
+  /// Removes the toast on screen, if any.
+  static void hide() {
+    final OverlayEntry? entry = _current;
+    _current = null;
+    if (entry != null && entry.mounted) entry.remove();
+  }
+}
+
+class _ToastView extends StatefulWidget {
+  const _ToastView({
+    required this.action,
+    required this.message,
+    required this.onDone,
+  });
+
+  final ShowToastAction action;
+  final String message;
+  final VoidCallback onDone;
+
+  @override
+  State<_ToastView> createState() => _ToastViewState();
+}
+
+class _ToastViewState extends State<_ToastView> {
+  static const Duration _fade = Duration(milliseconds: 220);
+
+  bool _visible = false;
+  Timer? _timer;
+
+  @override
+  void initState() {
+    super.initState();
+    WidgetsBinding.instance.addPostFrameCallback((_) {
+      if (mounted) setState(() => _visible = true);
+    });
+    _timer = Timer(Duration(milliseconds: widget.action.duration), () {
+      if (!mounted) return;
+      setState(() => _visible = false);
+      _timer = Timer(_fade, widget.onDone);
+    });
+  }
+
+  @override
+  void dispose() {
+    _timer?.cancel();
+    super.dispose();
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    final ShowToastAction action = widget.action;
+    final Color textColor = action.textColor.toFlutterColor();
+    final Widget? icon = action.icon == null
+        ? null
+        : retrieveIconWidget(action.icon!, 18);
+    return Positioned(
+      left: 16,
+      right: 16,
+      bottom: action.bottomOffset,
+      child: IgnorePointer(
+        child: Semantics(
+          liveRegion: true,
+          label: widget.message,
+          child: AnimatedOpacity(
+            opacity: _visible ? 1 : 0,
+            duration: _fade,
+            child: Center(
+              child: Material(
+                type: MaterialType.transparency,
+                child: Container(
+                  padding: const EdgeInsets.symmetric(
+                    horizontal: 18,
+                    vertical: 12,
+                  ),
+                  decoration: BoxDecoration(
+                    color: action.backgroundColor.toFlutterColor(),
+                    borderRadius: BorderRadius.circular(999),
+                    boxShadow: const [
+                      BoxShadow(
+                        color: Color(0x33000000),
+                        blurRadius: 18,
+                        offset: Offset(0, 6),
+                      ),
+                    ],
+                  ),
+                  child: Row(
+                    mainAxisSize: MainAxisSize.min,
+                    children: [
+                      if (icon != null) ...[icon, const SizedBox(width: 8)],
+                      Flexible(
+                        child: Text(
+                          widget.message,
+                          style: DefaultTextStyle.of(context).style.copyWith(
+                            color: textColor,
+                            fontSize: 14,
+                            fontWeight: FontWeight.w600,
+                            decoration: TextDecoration.none,
+                          ),
+                        ),
+                      ),
+                    ],
+                  ),
+                ),
+              ),
+            ),
+          ),
+        ),
+      ),
+    );
+  }
+}
diff --git a/lib/src/functions/functions_repository.dart b/lib/src/functions/functions_repository.dart
index 4537e3e2..8ca0a6d2 100644
--- a/lib/src/functions/functions_repository.dart
+++ b/lib/src/functions/functions_repository.dart
@@ -15,6 +15,7 @@ import '../logging/stat_tracker.dart';
 import '../ui/codelessly_dialog_widget.dart';
 import 'action_chain.dart';
 import 'app_auth.dart';
+import 'app_toast.dart';
 import 'cloud_files.dart';
 
 /// Enum representing the types of API requests.
@@ -134,6 +135,8 @@ class FunctionsRepository {
           action as CloudFilesAction,
           runActions: (actions) => runActions(context, actions),
         );
+      case ActionType.showToast:
+        return AppToast.show(context, action as ShowToastAction);
     }
   }
 
@@ -942,6 +945,48 @@ ${response.body.contains('{') ? const JsonEncoder.withIndent('  ').convert(json.
     payload.nodeValues[action.nodeID]!.set(updateValues, notify: notify);
   }
 
+  /// Substitutes variables in the [template] of a value to set. For list and
+  /// map values written as JSON, each JSON value is substituted on its own
+  /// (see [PropertyValueDelegate.substituteJsonValue]), so text holding
+  /// quotes or newlines can't break the JSON. Everything else is substituted
+  /// as text.
+  static String substituteNewValue(
+    String template,
+    VariableType type,
+    ScopedValues scopedValues,
+  ) {
+    if (type.isList || type.isMap) {
+      // A whole-value formula such as `${= item}` keeps its list or map.
+      final String? expression = FormulaEvaluator.exactExpression(template);
+      if (expression != null) {
+        final Object? value = PropertyValueDelegate.evaluateFormula(
+          expression,
+          scopedValues: scopedValues,
+        );
+        if (value is List || value is Map) {
+          return jsonEncode(
+            value,
+            toEncodable: (value) =>
+                value is DateTime ? value.toIso8601String() : value.toString(),
+          );
+        }
+      }
+      final Object? parsed = tryJsonDecode(template.trim());
+      if (parsed is List || parsed is Map) {
+        return jsonEncode(
+          PropertyValueDelegate.substituteJsonValue(parsed, scopedValues),
+          toEncodable: (value) =>
+              value is DateTime ? value.toIso8601String() : value.toString(),
+        );
+      }
+    }
+    return PropertyValueDelegate.substituteVariables(
+      template,
+      nullSubstitutionMode: NullSubstitutionMode.emptyString,
+      scopedValues: scopedValues,
+    );
+  }
+
   /// Sets given [action.newValue] for given [action.variable] to a variable
   /// from [CodelesslyContext.variables].
   /// Returns `true` if variable was found and updated, `false` otherwise.
@@ -958,10 +1003,10 @@ ${response.body.contains('{') ? const JsonEncoder.withIndent('  ').convert(json.
     );
     if (variableNotifier == null) return false;
 
-    String newValue = PropertyValueDelegate.substituteVariables(
+    String newValue = substituteNewValue(
       action.newValue,
-      nullSubstitutionMode: NullSubstitutionMode.emptyString,
-      scopedValues: scopedValues,
+      variableNotifier.value.type,
+      scopedValues,
     );
 
     Object? currentValue = variableNotifier.value.getValue();
@@ -1275,10 +1320,10 @@ ${response.body.contains('{') ? const JsonEncoder.withIndent('  ').convert(json.
         scopedValues: scopedValues,
       );
 
-      final newValue = PropertyValueDelegate.substituteVariables(
+      final newValue = substituteNewValue(
         action.newValue,
-        nullSubstitutionMode: NullSubstitutionMode.emptyString,
-        scopedValues: scopedValues,
+        action.variableType,
+        scopedValues,
       );
 
       final match = VariableMatch.parse(storageKey.wrapWithVariableSyntax());
diff --git a/lib/src/transformers/passive_transformer_manager.dart b/lib/src/transformers/passive_transformer_manager.dart
index e62cd531..7c0108c1 100644
--- a/lib/src/transformers/passive_transformer_manager.dart
+++ b/lib/src/transformers/passive_transformer_manager.dart
@@ -1,3 +1,5 @@
+import 'dart:math' as math;
+
 import 'package:codelessly_api/codelessly_api.dart';
 import 'package:collection/collection.dart';
 import 'package:flutter/material.dart';
@@ -78,29 +80,31 @@ class PassiveNodeTransformerManager extends WidgetNodeTransformerManager {
       context,
       node: node,
       builder: (context) {
+        final BaseNode styled = applyStyleOverrides(context, node);
         Widget widget = getTransformerByNode(node)
-            .buildWidget(node, context, settings);
+            .buildWidget(styled, context, settings);
 
         if (settings.withOpacity) {
-          widget = applyWidgetOpacity(node, widget);
+          widget = applyWidgetOpacity(styled, widget);
         }
         if (settings.withReactions) {
-          widget = wrapWithReaction(context, node, widget);
+          widget = wrapWithReaction(context, styled, widget);
+          widget = wrapWithSemantics(styled, widget);
         }
         if (settings.withRotation) {
-          widget = applyWidgetRotation(context, node, widget);
+          widget = applyWidgetRotation(context, styled, widget);
         }
         if (settings.withConstraints) {
-          widget = applyWidgetConstraints(node, widget);
+          widget = applyWidgetConstraints(styled, widget);
         }
         if (settings.withMargins) {
-          widget = applyWidgetMargins(node, widget);
+          widget = applyWidgetMargins(styled, widget);
         }
 
         if (settings.withVisibility) {
           widget = applyWidgetVisibility(
             context,
-            node,
+            styled,
             widget,
             maintainState: true,
           );
@@ -111,6 +115,81 @@ class PassiveNodeTransformerManager extends WidgetNodeTransformerManager {
     );
   }
 
+  /// Returns [node] with the style properties that conditions, bound
+  /// variables or formulas, or set value actions give it at runtime: `fill`
+  /// (a text's color for text nodes), `stroke`, `opacity`, `width` and
+  /// `height`. Returns [node] itself when
+  /// nothing changes it.
+  BaseNode applyStyleOverrides(BuildContext context, BaseNode node) {
+    final ScopedValues scopedValues = ScopedValues.of(context);
+    T? value<T extends Object>(String property) =>
+        PropertyValueDelegate.getPropertyValue<T>(
+          node,
+          property,
+          scopedValues: scopedValues,
+        );
+
+    final Map<String, dynamic> patch = {};
+    if (node is GeometryMixin) {
+      final GeometryMixin geometry = node;
+      final PaintModel? fill = value<PaintModel>('fill');
+      if (fill != null && fill != geometry.fills.firstOrNull) {
+        patch['fills'] = [
+          fill.copyWith(visible: true).toJson(),
+          for (final paint in geometry.fills.skip(1)) paint.toJson(),
+        ];
+      }
+      final PaintModel? stroke = value<PaintModel>('stroke');
+      if (stroke != null && stroke != geometry.strokes.firstOrNull) {
+        patch['strokes'] = [
+          stroke.copyWith(visible: true).toJson(),
+          for (final paint in geometry.strokes.skip(1)) paint.toJson(),
+        ];
+      }
+    }
+    if (node is TextNode) {
+      // A text's fill is its color: it replaces the color of every span.
+      final PaintModel? fill = value<PaintModel>('fill');
+      final PaintModel? current =
+          node.textMixedProps.firstOrNull?.fills.firstOrNull;
+      if (fill != null && fill != current) {
+        patch['textMixedProps'] = [
+          for (final prop in node.textMixedProps)
+            {
+              ...prop.toJson(),
+              'fills': [fill.copyWith(visible: true).toJson()],
+            },
+        ];
+      }
+    }
+    if (node is BlendMixin) {
+      final double? opacity = value<double>('opacity');
+      if (opacity != null && opacity != node.opacity) {
+        patch['opacity'] = opacity.clamp(0, 1).toDouble();
+      }
+    }
+    final NodeBox box = node.basicBoxLocal;
+    final double? width = value<double>('width');
+    final double? height = value<double>('height');
+    if ((width != null && width != box.width) ||
+        (height != null && height != box.height)) {
+      patch['basicBoxLocal'] = NodeBox(
+        box.x,
+        box.y,
+        math.max(0, width ?? box.width),
+        math.max(0, height ?? box.height),
+      ).toJson();
+    }
+
+    if (patch.isEmpty) return node;
+    final BaseNode? styled = NodeJsonConverter().fromJson({
+      ...node.toJson(),
+      ...patch,
+    });
+    if (styled == null) return node;
+    return styled..parentID = node.parentID;
+  }
+
   @override
   Widget buildWidgetByID(
     String id,
@@ -180,7 +259,15 @@ class PassiveNodeTransformerManager extends WidgetNodeTransformerManager {
 
     // Traverse through all the variables that the node properties are attached
     // to.
-    for (final String variablePath in node.variables.values.toSet()) {
+    // A property bound to a formula listens to the paths the formula reads.
+    final Set<String> boundPaths = {
+      for (final String path in node.variables.values)
+        if (FormulaEvaluator.exactExpression(path) case final String expression)
+          ...FormulaEvaluator.referencedPaths(expression)
+        else
+          path,
+    };
+    for (final String variablePath in boundPaths) {
       final match = VariableMatch.parse(variablePath.wrapWithVariableSyntax());
       if (match == null) continue;
 
@@ -218,6 +305,8 @@ class PassiveNodeTransformerManager extends WidgetNodeTransformerManager {
             .allMatches(node.characters)
             .map((match) => match.namedGroup('value'))
             .nonNulls,
+      if (node is TextNode)
+        ...FormulaEvaluator.referencedPathsInText(node.characters),
     };
     for (final String variablePath in multiplePaths) {
       final match = VariableMatch.parse(variablePath.wrapWithVariableSyntax());
diff --git a/lib/src/transformers/utils/condition_evaluator.dart b/lib/src/transformers/utils/condition_evaluator.dart
index cd579546..ce0cf1d5 100644
--- a/lib/src/transformers/utils/condition_evaluator.dart
+++ b/lib/src/transformers/utils/condition_evaluator.dart
@@ -62,6 +62,14 @@ class ConditionEvaluator<R extends Object>
     // A part that is exactly one path compares by its value as is, so lists
     // and maps keep their type for operators like contains and isEmpty.
     final String path = part.valueString.trim();
+    // A part that is exactly one formula keeps its value's type too.
+    final String? expression = FormulaEvaluator.exactExpression(path);
+    if (expression != null) {
+      return PropertyValueDelegate.evaluateFormula(
+        expression,
+        scopedValues: scopedValues,
+      );
+    }
     if (RegExp(r'^\$\{[^{}]+\}$').hasMatch(path)) {
       final Object? raw =
           PropertyValueDelegate.getVariableValueFromPath<Object>(
@@ -70,17 +78,26 @@ class ConditionEvaluator<R extends Object>
           );
       if (raw is List || raw is Map) return raw;
     }
-    final value = part.valueString.splitMapJoinRegex(
-      variablePathRegex,
-      onMatch: (match) {
-        final Object? value = PropertyValueDelegate.getVariableValueFromPath(
-          match[0]!,
-          scopedValues: scopedValues,
+    final value =
+        FormulaEvaluator.substitute(
+          part.valueString,
+          (path) => PropertyValueDelegate.getVariableValueFromPath<Object>(
+            path,
+            scopedValues: scopedValues,
+          ),
+          nullText: 'null',
+        ).splitMapJoinRegex(
+          variablePathRegex,
+          onMatch: (match) {
+            final Object? value =
+                PropertyValueDelegate.getVariableValueFromPath(
+                  match[0]!,
+                  scopedValues: scopedValues,
+                );
+
+            return value?.typedValue<String>() ?? 'null';
+          },
         );
-
-        return value?.typedValue<String>() ?? 'null';
-      },
-    );
     return _visitRawValue(value);
   }
 
@@ -251,6 +268,9 @@ class ConditionEvaluator<R extends Object>
   @override
   R? visitLinkAction(LinkAction action) => null;
 
+  @override
+  R? visitShowToastAction(ShowToastAction action) => null;
+
   @override
   R? visitNavigationAction(NavigationAction action) => null;
 
@@ -362,6 +382,9 @@ class ConditionPrinter
   @override
   void visitLinkAction(LinkAction action) {}
 
+  @override
+  void visitShowToastAction(ShowToastAction action) {}
+
   @override
   void visitNavigationAction(NavigationAction action) {}
 
diff --git a/lib/src/transformers/utils/condition_visitors.dart b/lib/src/transformers/utils/condition_visitors.dart
index 1564dd06..dadcbba3 100644
--- a/lib/src/transformers/utils/condition_visitors.dart
+++ b/lib/src/transformers/utils/condition_visitors.dart
@@ -1,5 +1,7 @@
 import 'package:codelessly_api/codelessly_api.dart';
 
+import '../../utils/formula.dart';
+
 /// A visitor that returns the list of variable names used in a condition.
 class ConditionVariablesVisitor
     implements
@@ -62,12 +64,14 @@ class ConditionVariablesVisitor
 
   @override
   Set<String> visitVariablePart(VariablePart part) {
-    return variablePathRegex
-        .allMatches(part.valueString)
-        .map((match) => match.namedGroup('name'))
-        .nonNulls
-        .where((element) => !excludedVariableNames.contains(element))
-        .toSet();
+    return {
+      ...variablePathRegex
+          .allMatches(part.valueString)
+          .map((match) => match.namedGroup('name'))
+          .nonNulls,
+      ...FormulaEvaluator.referencedPathsInText(part.valueString)
+          .map((path) => path.split(RegExp(r'[.\[]')).first),
+    }.where((element) => !excludedVariableNames.contains(element)).toSet();
   }
 
   @override
@@ -79,6 +83,9 @@ class ConditionVariablesVisitor
   @override
   Set<String>? visitLinkAction(LinkAction action) => {};
 
+  @override
+  Set<String>? visitShowToastAction(ShowToastAction action) => {};
+
   @override
   Set<String>? visitNavigationAction(NavigationAction action) => {};
 
@@ -169,6 +176,9 @@ class ConditionNodesVisitor
   @override
   String? visitLinkAction(LinkAction action) => null;
 
+  @override
+  String? visitShowToastAction(ShowToastAction action) => null;
+
   @override
   String? visitNavigationAction(NavigationAction action) => null;
 
diff --git a/lib/src/transformers/utils/property_value_delegate.dart b/lib/src/transformers/utils/property_value_delegate.dart
index 3be42119..6bee63c4 100644
--- a/lib/src/transformers/utils/property_value_delegate.dart
+++ b/lib/src/transformers/utils/property_value_delegate.dart
@@ -174,11 +174,23 @@ class PropertyValueDelegate {
     );
   }
 
+  /// Substitutes variables in a decoded JSON [value]: see
+  /// [substituteVariablesInJson].
+  static Object? substituteJsonValue(
+    Object? value,
+    ScopedValues scopedValues,
+  ) => _substituteJsonValue(value, scopedValues);
+
   static Object? _substituteJsonValue(
     Object? value,
     ScopedValues scopedValues,
   ) {
     return switch (value) {
+      String() when FormulaEvaluator.exactExpression(value) != null =>
+        evaluateFormula(
+          FormulaEvaluator.exactExpression(value)!,
+          scopedValues: scopedValues,
+        ),
       String() =>
         RegExp(r'^\$\{[^{}]+\}$').hasMatch(value.trim())
             ? _retrieveVariableValue(value.trim(), scopedValues: scopedValues)
@@ -211,6 +223,16 @@ class PropertyValueDelegate {
     required NullSubstitutionMode nullSubstitutionMode,
   }) {
     if (text.trim().isEmpty) return text;
+    // Formulas first, so `${= ...}` isn't read as a path.
+    text = FormulaEvaluator.substitute(
+      text,
+      (path) =>
+          getVariableValueFromPath<Object>(path, scopedValues: scopedValues),
+      nullText: switch (nullSubstitutionMode) {
+        NullSubstitutionMode.nullValue => 'null',
+        _ => '',
+      },
+    );
     return text.splitMapJoinRegex(
       variablePathRegex,
       onNonMatch: (text) => text,
@@ -232,6 +254,17 @@ class PropertyValueDelegate {
     );
   }
 
+  /// Evaluates a formula [expression] (the part after `${=`), reading its
+  /// variable paths from [scopedValues]. See [FormulaEvaluator].
+  static Object? evaluateFormula(
+    String expression, {
+    required ScopedValues scopedValues,
+  }) => FormulaEvaluator.evaluate(
+    expression,
+    (path) =>
+        getVariableValueFromPath<Object>(path, scopedValues: scopedValues),
+  );
+
   /// Retrieves the value of a variable [path]. This also supports predefined
   /// variables such as data, index, and item.
   ///
@@ -246,6 +279,15 @@ class PropertyValueDelegate {
     String path, {
     required ScopedValues scopedValues,
   }) {
+    final String? expression = FormulaEvaluator.exactExpression(path);
+    if (expression != null) {
+      final Object? value = evaluateFormula(
+        expression,
+        scopedValues: scopedValues,
+      );
+      if (R == String) return FormulaEvaluator.stringify(value) as R?;
+      return value?.typedValue<R>();
+    }
     final match = VariableMatch.parse(path.wrapWithVariableSyntax());
     if (match == null) return null;
 
diff --git a/lib/src/transformers/widget_node_transformer_manager.dart b/lib/src/transformers/widget_node_transformer_manager.dart
index 93c04537..99ada0f5 100644
--- a/lib/src/transformers/widget_node_transformer_manager.dart
+++ b/lib/src/transformers/widget_node_transformer_manager.dart
@@ -131,6 +131,73 @@ abstract class WidgetNodeTransformerManager
     );
   }
 
+  static final RegExp _defaultNodeName = RegExp(
+    r'^(frame|rectangle|row|column|stack|group|icon|container|ellipse|image|'
+    r'auto layout|layout|node)\s*\d*$',
+    caseSensitive: false,
+  );
+
+  /// Tells screen readers that a tappable node is a button. A node with text
+  /// inside reads as that text; one without (an icon button) reads as its
+  /// node name, or its icon's name when the node still has a default name.
+  Widget wrapWithSemantics(BaseNode node, Widget widget) {
+    if (node is! ReactionMixin) return widget;
+    if (node case CanvasNode() || SpacerNode()) return widget;
+    if (node is CustomPropertiesMixin &&
+        node.handlesDefaultReactionsInternally) {
+      return widget;
+    }
+    final bool tappable = (node as ReactionMixin).reactions.any(
+      (reaction) =>
+          reaction.trigger.type == TriggerType.click && reaction.action.enabled,
+    );
+    if (!tappable) return widget;
+
+    final List<BaseNode> descendants = [];
+    void collect(BaseNode parent) {
+      for (final String id in parent.childrenOrEmpty) {
+        final BaseNode? child = _tryGetNode(id);
+        if (child == null) continue;
+        descendants.add(child);
+        collect(child);
+      }
+    }
+
+    collect(node);
+
+    final bool hasText = descendants.any((child) => child is TextNode);
+    final String label = hasText ? '' : semanticLabelFor(node, descendants);
+    return MergeSemantics(
+      child: Semantics(
+        button: true,
+        label: label.isEmpty ? null : label,
+        child: widget,
+      ),
+    );
+  }
+
+  /// The name a screen reader announces for [node] when it has no text.
+  static String semanticLabelFor(BaseNode node, List<BaseNode> descendants) {
+    final String name = node.name.trim();
+    if (name.isNotEmpty && !_defaultNodeName.hasMatch(name)) return name;
+    for (final BaseNode child in descendants) {
+      if (child is! IconNode) continue;
+      final String? iconName = child.properties.icon.icon?.name;
+      if (iconName != null && iconName.isNotEmpty) {
+        return iconName.replaceAll('_', ' ');
+      }
+    }
+    return '';
+  }
+
+  BaseNode? _tryGetNode(String id) {
+    try {
+      return getNode(id);
+    } catch (_) {
+      return null;
+    }
+  }
+
   /// Convenience method to handle widget reactions.
   Widget wrapWithReaction(BuildContext context, BaseNode node, Widget widget) {
     if (node is! ReactionMixin) return widget;
@@ -175,11 +242,13 @@ abstract class WidgetNodeTransformerManager
             TriggerType.click,
             reactions: onClickReactions,
           ),
-          onLongPress: () => FunctionsRepository.triggerAction(
-            context,
-            TriggerType.longPress,
-            reactions: onLongPressReactions,
-          ),
+          onLongPress: onLongPressReactions.isEmpty
+              ? null
+              : () => FunctionsRepository.triggerAction(
+                  context,
+                  TriggerType.longPress,
+                  reactions: onLongPressReactions,
+                ),
           borderRadius: getBorderRadius(node),
           overlayColor: inkWell.overlayColor != null
               ? WidgetStatePropertyAll<Color>(
@@ -208,11 +277,13 @@ abstract class WidgetNodeTransformerManager
             TriggerType.click,
             reactions: onClickReactions,
           ),
-          onLongPress: () => FunctionsRepository.triggerAction(
-            context,
-            TriggerType.longPress,
-            reactions: onLongPressReactions,
-          ),
+          onLongPress: onLongPressReactions.isEmpty
+              ? null
+              : () => FunctionsRepository.triggerAction(
+                  context,
+                  TriggerType.longPress,
+                  reactions: onLongPressReactions,
+                ),
           child: widget,
         ),
       );
diff --git a/lib/src/utils/extensions.dart b/lib/src/utils/extensions.dart
index cb4e2d53..08ab9da9 100644
--- a/lib/src/utils/extensions.dart
+++ b/lib/src/utils/extensions.dart
@@ -1679,6 +1679,9 @@ extension ActionModelExt on ActionModel {
       case ActionType.link:
         final LinkAction action = this as LinkAction;
         strings.addAll([action.url]);
+      case ActionType.showToast:
+        final ShowToastAction action = this as ShowToastAction;
+        strings.addAll([action.message]);
       case ActionType.submit:
         final SubmitAction action = this as SubmitAction;
         strings.addAll([action.apiKey, action.primaryTextField]);
diff --git a/lib/src/utils/formula.dart b/lib/src/utils/formula.dart
new file mode 100644
index 00000000..9425995b
--- /dev/null
+++ b/lib/src/utils/formula.dart
@@ -0,0 +1,687 @@
+import 'dart:math' as math;
+
+/// Matches a formula written as `${= expression}` in a text.
+///
+/// The expression can't contain braces, except inside quoted strings.
+final RegExp formulaRegex = RegExp(
+  r'''(?<!\\)\$\{=(?<expr>(?:[^{}'"]|'[^']*'|"[^"]*")*)\}''',
+);
+
+/// Matches a text that is exactly one formula, e.g. `${= qty * price}`.
+final RegExp exactFormulaRegex = RegExp(
+  r'''^\s*(?<!\\)\$\{=(?<expr>(?:[^{}'"]|'[^']*'|"[^"]*")*)\}\s*$''',
+);
+
+/// Resolves a variable path such as `storage.cart` or `item.price` to its
+/// value.
+typedef FormulaPathResolver = Object? Function(String path);
+
+/// Evaluates small expressions used in `${= ...}` formulas.
+///
+/// Supports:
+///  - numbers, 'single' or "double" quoted strings, true, false, null and
+///    `[a, b]` lists.
+///  - variable paths like `storage.cart.length` or `item.price`, resolved with
+///    the same rules as `${path}`, followed by `[index]` or `.key`.
+///  - `+ - * / %`, comparisons `== != < <= > >=`, `&& || !` and
+///    `condition ? a : b`. `+` joins text when either side is text.
+///  - functions: money, fixed, round, floor, ceil, abs, min, max, sum, count,
+///    length, if, plural, join, upper, lower, contains, where, without,
+///    number, text, isEmpty and isNotEmpty. See [FormulaEvaluator.functions].
+///
+/// Null counts as 0 in arithmetic and as empty text when joining text. An
+/// invalid expression evaluates to null.
+class FormulaEvaluator {
+  const FormulaEvaluator._();
+
+  static final Map<String, _Node?> _cache = {};
+
+  /// Evaluates [expression], resolving variable paths with [resolve].
+  static Object? evaluate(String expression, FormulaPathResolver resolve) {
+    final _Node? node = _parse(expression);
+    if (node == null) return null;
+    try {
+      return node.eval(resolve);
+    } catch (_) {
+      return null;
+    }
+  }
+
+  /// The variable paths [expression] reads, e.g. `storage.cart` and `qty`.
+  static Set<String> referencedPaths(String expression) {
+    final _Node? node = _parse(expression);
+    if (node == null) return {};
+    final Set<String> paths = {};
+    node.collectPaths(paths);
+    return paths;
+  }
+
+  /// The variable paths read by every formula in [text].
+  static Set<String> referencedPathsInText(String text) => {
+    for (final match in formulaRegex.allMatches(text))
+      ...referencedPaths(match.namedGroup('expr')!),
+  };
+
+  /// Replaces every `${= ...}` formula in [text] with its result as text.
+  /// A formula that evaluates to null becomes [nullText].
+  static String substitute(
+    String text,
+    FormulaPathResolver resolve, {
+    String nullText = '',
+  }) {
+    if (!text.contains(r'${=')) return text;
+    return text.splitMapJoin(
+      formulaRegex,
+      onMatch: (match) {
+        final Object? value = evaluate(
+          (match as RegExpMatch).namedGroup('expr')!,
+          resolve,
+        );
+        return value == null ? nullText : stringify(value);
+      },
+      onNonMatch: (text) => text,
+    );
+  }
+
+  /// The expression of [text] when it is exactly one formula, else null.
+  static String? exactExpression(String text) =>
+      exactFormulaRegex.firstMatch(text)?.namedGroup('expr');
+
+  /// Formats [value] as text: whole numbers drop their decimals and other
+  /// numbers lose floating point noise, e.g. 17.200000000000003 is "17.2".
+  static String stringify(Object? value) {
+    if (value == null) return '';
+    if (value is num) {
+      if (value.isNaN || value.isInfinite) return '';
+      if (value == value.roundToDouble()) return value.toInt().toString();
+      String text = value.toStringAsFixed(10);
+      text = text.replaceFirst(RegExp(r'0+$'), '');
+      return text.endsWith('.') ? text.substring(0, text.length - 1) : text;
+    }
+    if (value is List) return value.map(stringify).join(', ');
+    return value.toString();
+  }
+
+  /// Parses [expression], caching the result. Returns null when it's invalid.
+  static _Node? _parse(String expression) {
+    final String key = expression.trim();
+    if (_cache.containsKey(key)) return _cache[key];
+    _Node? node;
+    try {
+      node = _Parser(key).parseAll();
+    } catch (_) {
+      node = null;
+    }
+    if (_cache.length > 2000) _cache.clear();
+    return _cache[key] = node;
+  }
+
+  /// Names of the functions formulas can call.
+  static Iterable<String> get functions => _functions.keys;
+}
+
+// ---------------------------------------------------------------------------
+// Values
+// ---------------------------------------------------------------------------
+
+bool _truthy(Object? value) => switch (value) {
+  null => false,
+  bool() => value,
+  num() => value != 0,
+  String() => value.isNotEmpty && value.toLowerCase() != 'false',
+  Iterable() => value.isNotEmpty,
+  Map() => value.isNotEmpty,
+  _ => true,
+};
+
+/// Reads [value] as a number: numbers as is, numeric text parsed, null as 0.
+num? _toNum(Object? value) => switch (value) {
+  null => 0,
+  num() => value,
+  bool() => value ? 1 : 0,
+  String() => value.trim().isEmpty ? 0 : num.tryParse(value.trim()),
+  _ => null,
+};
+
+num _num(Object? value) => _toNum(value) ?? double.nan;
+
+/// Keeps whole results as ints so `2 * 3` prints "6".
+num _tidy(num value) =>
+    value is double && value.isFinite && value == value.roundToDouble()
+    ? value.toInt()
+    : value;
+
+bool _looseEquals(Object? a, Object? b) {
+  if (a == null || b == null) return a == b;
+  final num? na = a is String ? num.tryParse(a) : _toNum(a);
+  final num? nb = b is String ? num.tryParse(b) : _toNum(b);
+  if ((a is num || b is num) && na != null && nb != null) return na == nb;
+  if (a is bool || b is bool) return _truthy(a) == _truthy(b);
+  return a.toString() == b.toString();
+}
+
+int _compare(Object? a, Object? b) {
+  final num? na = a is String ? num.tryParse(a) : _toNum(a);
+  final num? nb = b is String ? num.tryParse(b) : _toNum(b);
+  if (na != null && nb != null) return na.compareTo(nb);
+  return (a?.toString() ?? '').compareTo(b?.toString() ?? '');
+}
+
+Object? _member(Object? target, Object? key) {
+  if (target == null) return null;
+  if (target is List) {
+    if (key == 'length') return target.length;
+    if (key == 'first') return target.isEmpty ? null : target.first;
+    if (key == 'last') return target.isEmpty ? null : target.last;
+    final num? index = _toNum(key);
+    if (index == null) return null;
+    final int i = index.toInt();
+    return i >= 0 && i < target.length ? target[i] : null;
+  }
+  if (target is Map) {
+    if (target.containsKey(key)) return target[key];
+    if (key == 'length') return target.length;
+    return target[key.toString()];
+  }
+  if (target is String) {
+    if (key == 'length') return target.length;
+    final num? index = _toNum(key);
+    if (index == null) return null;
+    final int i = index.toInt();
+    return i >= 0 && i < target.length ? target[i] : null;
+  }
+  return null;
+}
+
+String _fixed(Object? value, Object? digits) =>
+    _num(value).toStringAsFixed(_num(digits ?? 2).toInt().clamp(0, 20));
+
+String _money(Object? value, Object? symbol) {
+  final num amount = _num(value);
+  if (amount.isNaN) return '';
+  final String sign = amount < 0 ? '-' : '';
+  final String text = amount.abs().toStringAsFixed(2);
+  final int dot = text.indexOf('.');
+  final String whole = text
+      .substring(0, dot)
+      .replaceAllMapped(RegExp(r'\B(?=(\d{3})+(?!\d))'), (_) => ',');
+  return '$sign${symbol ?? r'$'}$whole${text.substring(dot)}';
+}
+
+num _round(Object? value, Object? digits) {
+  final num v = _num(value);
+  final int d = _num(digits ?? 0).toInt();
+  if (d <= 0) return v.round();
+  final num factor = math.pow(10, d);
+  return _tidy((v * factor).round() / factor);
+}
+
+/// Values of [list], or of each item's [field] when given.
+Iterable<Object?> _values(Object? list, Object? field) {
+  if (list is! Iterable) return const [];
+  if (field == null) return list;
+  return list.map((item) => _member(item, field));
+}
+
+typedef _Function = Object? Function(List<Object?> args);
+
+Object? _arg(List<Object?> args, int index) =>
+    index < args.length ? args[index] : null;
+
+final Map<String, _Function> _functions = {
+  'money': (a) => _money(_arg(a, 0), _arg(a, 1)),
+  'fixed': (a) => _fixed(_arg(a, 0), _arg(a, 1)),
+  'round': (a) => _round(_arg(a, 0), _arg(a, 1)),
+  'floor': (a) => _num(_arg(a, 0)).floor(),
+  'ceil': (a) => _num(_arg(a, 0)).ceil(),
+  'abs': (a) => _num(_arg(a, 0)).abs(),
+  'min': (a) => (a.length == 1 && a.first is Iterable ? a.first as Iterable : a)
+      .map(_num)
+      .reduce(math.min),
+  'max': (a) => (a.length == 1 && a.first is Iterable ? a.first as Iterable : a)
+      .map(_num)
+      .reduce(math.max),
+  'sum': (a) => _tidy(
+    _values(_arg(a, 0), _arg(a, 1)).fold<num>(0, (s, v) => s + _num(v)),
+  ),
+  'count': (a) {
+    if (a.length < 3) return _values(_arg(a, 0), null).length;
+    return _values(
+      _arg(a, 0),
+      _arg(a, 1),
+    ).where((v) => _looseEquals(v, _arg(a, 2))).length;
+  },
+  'length': (a) => switch (_arg(a, 0)) {
+    final String s => s.length,
+    final Iterable l => l.length,
+    final Map m => m.length,
+    _ => 0,
+  },
+  'if': (a) => _truthy(_arg(a, 0)) ? _arg(a, 1) : _arg(a, 2),
+  'plural': (a) =>
+      _num(_arg(a, 0)) == 1 ? _arg(a, 1) : (_arg(a, 2) ?? '${_arg(a, 1)}s'),
+  'join': (a) => _values(_arg(a, 0), _arg(a, 2))
+      .map(FormulaEvaluator.stringify)
+      .where((s) => s.isNotEmpty)
+      .join((_arg(a, 1) ?? ', ').toString()),
+  'upper': (a) => FormulaEvaluator.stringify(_arg(a, 0)).toUpperCase(),
+  'lower': (a) => FormulaEvaluator.stringify(_arg(a, 0)).toLowerCase(),
+  'contains': (a) => switch (_arg(a, 0)) {
+    final String s => s.contains(FormulaEvaluator.stringify(_arg(a, 1))),
+    final Iterable l => l.any((v) => _looseEquals(v, _arg(a, 1))),
+    final Map m => m.containsKey(_arg(a, 1)),
+    _ => false,
+  },
+  'where': (a) => [
+    for (final item in _values(_arg(a, 0), null))
+      if (a.length < 3
+          ? _truthy(_member(item, _arg(a, 1)))
+          : _looseEquals(_member(item, _arg(a, 1)), _arg(a, 2)))
+        item,
+  ],
+  'without': (a) => [
+    for (final item in _values(_arg(a, 0), null))
+      if (!_values(_arg(a, 1), null).any((other) => _looseEquals(item, other)))
+        item,
+  ],
+  'number': (a) => _toNum(_arg(a, 0)),
+  'text': (a) => FormulaEvaluator.stringify(_arg(a, 0)),
+  'isEmpty': (a) => !_truthy(_functions['length']!(a)),
+  'isNotEmpty': (a) => _truthy(_functions['length']!(a)),
+};
+
+// ---------------------------------------------------------------------------
+// Syntax tree
+// ---------------------------------------------------------------------------
+
+sealed class _Node {
+  const _Node();
+
+  Object? eval(FormulaPathResolver resolve);
+
+  void collectPaths(Set<String> paths) {}
+}
+
+class _Literal extends _Node {
+  final Object? value;
+
+  const _Literal(this.value);
+
+  @override
+  Object? eval(FormulaPathResolver resolve) => value;
+}
+
+class _Path extends _Node {
+  final String path;
+
+  const _Path(this.path);
+
+  @override
+  Object? eval(FormulaPathResolver resolve) => resolve(path);
+
+  @override
+  void collectPaths(Set<String> paths) => paths.add(path);
+}
+
+class _ListLiteral extends _Node {
+  final List<_Node> items;
+
+  const _ListLiteral(this.items);
+
+  @override
+  Object? eval(FormulaPathResolver resolve) => [
+    for (final item in items) item.eval(resolve),
+  ];
+
+  @override
+  void collectPaths(Set<String> paths) {
+    for (final item in items) {
+      item.collectPaths(paths);
+    }
+  }
+}
+
+class _Member extends _Node {
+  final _Node target;
+  final _Node key;
+
+  const _Member(this.target, this.key);
+
+  @override
+  Object? eval(FormulaPathResolver resolve) =>
+      _member(target.eval(resolve), key.eval(resolve));
+
+  @override
+  void collectPaths(Set<String> paths) {
+    target.collectPaths(paths);
+    key.collectPaths(paths);
+  }
+}
+
+class _Call extends _Node {
+  final String name;
+  final List<_Node> args;
+
+  const _Call(this.name, this.args);
+
+  @override
+  Object? eval(FormulaPathResolver resolve) {
+    // `if` only evaluates the branch it returns.
+    if (name == 'if') {
+      _Node? arg(int i) => i < args.length ? args[i] : null;
+      return _truthy(arg(0)?.eval(resolve))
+          ? arg(1)?.eval(resolve)
+          : arg(2)?.eval(resolve);
+    }
+    return _functions[name]!([for (final arg in args) arg.eval(resolve)]);
+  }
+
+  @override
+  void collectPaths(Set<String> paths) {
+    for (final arg in args) {
+      arg.collectPaths(paths);
+    }
+  }
+}
+
+class _Unary extends _Node {
+  final String op;
+  final _Node operand;
+
+  const _Unary(this.op, this.operand);
+
+  @override
+  Object? eval(FormulaPathResolver resolve) {
+    final Object? value = operand.eval(resolve);
+    return op == '!' ? !_truthy(value) : _tidy(-_num(value));
+  }
+
+  @override
+  void collectPaths(Set<String> paths) => operand.collectPaths(paths);
+}
+
+class _Binary extends _Node {
+  final String op;
+  final _Node left;
+  final _Node right;
+
+  const _Binary(this.op, this.left, this.right);
+
+  @override
+  Object? eval(FormulaPathResolver resolve) {
+    final Object? a = left.eval(resolve);
+    if (op == '&&') return _truthy(a) ? right.eval(resolve) : a;
+    if (op == '||') return _truthy(a) ? a : right.eval(resolve);
+    final Object? b = right.eval(resolve);
+    switch (op) {
+      case '+':
+        final num? na = a is String ? null : _toNum(a);
+        final num? nb = b is String ? null : _toNum(b);
+        if (na != null && nb != null) return _tidy(na + nb);
+        return FormulaEvaluator.stringify(a) + FormulaEvaluator.stringify(b);
+      case '-':
+        return _tidy(_num(a) - _num(b));
+      case '*':
+        return _tidy(_num(a) * _num(b));
+      case '/':
+        final num divisor = _num(b);
+        return divisor == 0 ? null : _tidy(_num(a) / divisor);
+      case '%':
+        final num divisor = _num(b);
+        return divisor == 0 ? null : _tidy(_num(a) % divisor);
+      case '==':
+        return _looseEquals(a, b);
+      case '!=':
+        return !_looseEquals(a, b);
+      case '<':
+        return _compare(a, b) < 0;
+      case '<=':
+        return _compare(a, b) <= 0;
+      case '>':
+        return _compare(a, b) > 0;
+      case '>=':
+        return _compare(a, b) >= 0;
+    }
+    return null;
+  }
+
+  @override
+  void collectPaths(Set<String> paths) {
+    left.collectPaths(paths);
+    right.collectPaths(paths);
+  }
+}
+
+class _Ternary extends _Node {
+  final _Node condition;
+  final _Node then;
+  final _Node otherwise;
+
+  const _Ternary(this.condition, this.then, this.otherwise);
+
+  @override
+  Object? eval(FormulaPathResolver resolve) => _truthy(condition.eval(resolve))
+      ? then.eval(resolve)
+      : otherwise.eval(resolve);
+
+  @override
+  void collectPaths(Set<String> paths) {
+    condition.collectPaths(paths);
+    then.collectPaths(paths);
+    otherwise.collectPaths(paths);
+  }
+}
+
+// ---------------------------------------------------------------------------
+// Parser
+// ---------------------------------------------------------------------------
+
+class _Parser {
+  final String source;
+  int pos = 0;
+
+  _Parser(this.source);
+
+  static final RegExp _number = RegExp(r'\d+(\.\d+)?|\.\d+');
+  static final RegExp _identifier = RegExp(r'[a-zA-Z_][a-zA-Z0-9_]*');
+
+  _Node parseAll() {
+    final _Node node = _ternary();
+    _skip();
+    if (pos != source.length) {
+      throw FormatException('Unexpected "${source[pos]}"', source, pos);
+    }
+    return node;
+  }
+
+  void _skip() {
+    while (pos < source.length && source[pos].trim().isEmpty) {
+      pos++;
+    }
+  }
+
+  bool _eat(String token) {
+    _skip();
+    if (!source.startsWith(token, pos)) return false;
+    // Don't read `=` of `==` or `<=` as a separate token.
+    if ((token == '<' || token == '>' || token == '!') &&
+        source.startsWith('=', pos + 1)) {
+      return false;
+    }
+    pos += token.length;
+    return true;
+  }
+
+  void _expect(String token) {
+    if (!_eat(token)) throw FormatException('Expected "$token"', source, pos);
+  }
+
+  _Node _ternary() {
+    final _Node condition = _or();
+    if (!_eat('?')) return condition;
+    final _Node then = _ternary();
+    _expect(':');
+    return _Ternary(condition, then, _ternary());
+  }
+
+  _Node _or() {
+    _Node node = _and();
+    while (_eat('||')) {
+      node = _Binary('||', node, _and());
+    }
+    return node;
+  }
+
+  _Node _and() {
+    _Node node = _equality();
+    while (_eat('&&')) {
+      node = _Binary('&&', node, _equality());
+    }
+    return node;
+  }
+
+  _Node _equality() {
+    _Node node = _comparison();
+    while (true) {
+      if (_eat('==')) {
+        node = _Binary('==', node, _comparison());
+      } else if (_eat('!=')) {
+        node = _Binary('!=', node, _comparison());
+      } else {
+        return node;
+      }
+    }
+  }
+
+  _Node _comparison() {
+    _Node node = _additive();
+    while (true) {
+      final String? op = ['<=', '>=', '<', '>'].where(_eat).firstOrNull;
+      if (op == null) return node;
+      node = _Binary(op, node, _additive());
+    }
+  }
+
+  _Node _additive() {
+    _Node node = _multiplicative();
+    while (true) {
+      final String? op = ['+', '-'].where(_eat).firstOrNull;
+      if (op == null) return node;
+      node = _Binary(op, node, _multiplicative());
+    }
+  }
+
+  _Node _multiplicative() {
+    _Node node = _unary();
+    while (true) {
+      final String? op = ['*', '/', '%'].where(_eat).firstOrNull;
+      if (op == null) return node;
+      node = _Binary(op, node, _unary());
+    }
+  }
+
+  _Node _unary() {
+    if (_eat('!')) return _Unary('!', _unary());
+    if (_eat('-')) return _Unary('-', _unary());
+    return _postfix(_primary());
+  }
+
+  _Node _postfix(_Node node) {
+    while (true) {
+      if (_eat('[')) {
+        node = _Member(node, _ternary());
+        _expect(']');
+      } else if (_eat('.')) {
+        final Match? name = _identifier.matchAsPrefix(source, pos);
+        if (name == null) throw FormatException('Expected a name', source, pos);
+        pos = name.end;
+        node = _Member(node, _Literal(name[0]));
+      } else {
+        return node;
+      }
+    }
+  }
+
+  _Node _primary() {
+    _skip();
+    if (pos >= source.length) {
+      throw FormatException('Unexpected end', source, pos);
+    }
+    final String char = source[pos];
+
+    if (char == '(') {
+      pos++;
+      final _Node node = _ternary();
+      _expect(')');
+      return node;
+    }
+
+    if (char == '[') {
+      pos++;
+      final List<_Node> items = [];
+      if (!_eat(']')) {
+        do {
+          items.add(_ternary());
+        } while (_eat(','));
+        _expect(']');
+      }
+      return _ListLiteral(items);
+    }
+
+    if (char == "'" || char == '"') {
+      final int end = source.indexOf(char, pos + 1);
+      if (end < 0) throw FormatException('Unclosed text', source, pos);
+      final String text = source.substring(pos + 1, end);
+      pos = end + 1;
+      return _Literal(text);
+    }
+
+    final Match? number = _number.matchAsPrefix(source, pos);
+    if (number != null) {
+      pos = number.end;
+      return _Literal(num.parse(number[0]!));
+    }
+
+    final Match? identifier = _identifier.matchAsPrefix(source, pos);
+    if (identifier == null) {
+      throw FormatException('Unexpected "$char"', source, pos);
+    }
+    pos = identifier.end;
+    final String name = identifier[0]!;
+
+    switch (name) {
+      case 'true':
+        return const _Literal(true);
+      case 'false':
+        return const _Literal(false);
+      case 'null':
+        return const _Literal(null);
+    }
+
+    if (_eat('(')) {
+      if (!_functions.containsKey(name)) {
+        throw FormatException('Unknown function "$name"', source, pos);
+      }
+      final List<_Node> args = [];
+      if (!_eat(')')) {
+        do {
+          args.add(_ternary());
+        } while (_eat(','));
+        _expect(')');
+      }
+      return _Call(name, args);
+    }
+
+    // A variable path: name followed by `.key` and `[digits]` parts, read as
+    // one path so accessors like `.length` and `.initial` work as in `${}`.
+    final StringBuffer path = StringBuffer(name);
+    while (true) {
+      final Match? part = RegExp(r'\.[a-zA-Z][a-zA-Z0-9_]*|\[\d+\]')
+          .matchAsPrefix(source, pos);
+      if (part == null) break;
+      path.write(part[0]);
+      pos = part.end;
+    }
+    return _Path(path.toString());
+  }
+}
diff --git a/pubspec.yaml b/pubspec.yaml
index 219f375a..8429ee72 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -92,3 +92,12 @@ false_secrets:
   - /lib/src/firebase_options_prod.dart
 
 scripts: scripts.yaml
+
+# Temporary: the show toast action needs codelessly_api from
+# Codelessly/CodelesslyAPI#37, merged but not yet published. Remove once
+# codelessly_api is released.
+dependency_overrides:
+  codelessly_api:
+    git:
+      url: https://github.com/Codelessly/CodelesslyAPI.git
+      ref: master
diff --git a/test/formula_test.dart b/test/formula_test.dart
new file mode 100644
index 00000000..07426f83
--- /dev/null
+++ b/test/formula_test.dart
@@ -0,0 +1,218 @@
+import 'package:codelessly_api/codelessly_api.dart';
+import 'package:codelessly_sdk/codelessly_sdk.dart';
+import 'package:flutter/widgets.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  final Map<String, Object?> vars = {
+    'qty': 2,
+    'price': 5.25,
+    'name': 'Ava',
+    'shots': '3',
+    'cart': [
+      {'name': 'Cortado', 'qty': 1, 'total': 4.75},
+      {'name': 'Oat latte', 'qty': 2, 'total': 12.9},
+    ],
+    'syrups': ['vanilla', 'honey'],
+  };
+  Object? resolve(String path) {
+    final parts = RegExp(r'[a-zA-Z_]\w*|\d+').allMatches(path).toList();
+    Object? value = vars[parts.first[0]];
+    for (final part in parts.skip(1).map((m) => m[0]!)) {
+      value = switch (value) {
+        final List list when part == 'length' => list.length,
+        final List list => list[int.parse(part)],
+        final Map map => map[part],
+        _ => null,
+      };
+    }
+    return value;
+  }
+
+  Object? eval(String expression) =>
+      FormulaEvaluator.evaluate(expression, resolve);
+
+  group('FormulaEvaluator', () {
+    test('arithmetic and precedence', () {
+      expect(eval('1 + 2 * 3'), 7);
+      expect(eval('(1 + 2) * 3'), 9);
+      expect(eval('qty * price'), 10.5);
+      expect(eval('10 / 4'), 2.5);
+      expect(eval('10 / 0'), isNull);
+      expect(eval('7 % 3'), 1);
+      expect(eval('-qty + 1'), -1);
+      expect(eval('shots * 0.9'), closeTo(2.7, 1e-9));
+      expect(eval('missing + 1'), 1);
+    });
+
+    test('text', () {
+      expect(eval("'Hi ' + name"), 'Hi Ava');
+      expect(eval('"x" + 2'), 'x2');
+      expect(eval("upper(name) + lower('B')"), 'AVAb');
+      expect(eval("plural(qty, 'drink')"), 'drinks');
+      expect(eval("plural(1, 'drink')"), 'drink');
+      expect(eval("join(syrups, ' · ')"), 'vanilla · honey');
+      expect(eval("join(cart, ', ', 'name')"), 'Cortado, Oat latte');
+    });
+
+    test('comparisons, logic and ternary', () {
+      expect(eval('qty > 1 && price < 6'), true);
+      expect(eval('qty == 2'), true);
+      expect(eval('shots == 3'), true);
+      expect(eval("name != 'Ava'"), false);
+      expect(eval('!qty'), false);
+      expect(eval("qty > 1 ? 'many' : 'one'"), 'many');
+      expect(eval("qty > 5 ? 'a' : qty > 1 ? 'b' : 'c'"), 'b');
+      expect(eval('missing || 4'), 4);
+    });
+
+    test('functions', () {
+      expect(eval('money(qty * price)'), r'$10.50');
+      expect(eval('money(1234567.891)'), r'$1,234,567.89');
+      expect(eval("money(-3, '€')"), '-€3.00');
+      expect(eval('fixed(price, 1)'), '5.3');
+      expect(eval('round(2.345, 2)'), 2.35);
+      expect(eval('round(2.5)'), 3);
+      expect(eval('floor(2.9) + ceil(2.1)'), 5);
+      expect(eval('min(3, 1, 2)'), 1);
+      expect(eval('max([3, 9, 2])'), 9);
+      expect(eval("sum(cart, 'total')"), 17.65);
+      expect(eval("sum(cart, 'qty')"), 3);
+      expect(eval('count(cart)'), 2);
+      expect(eval("count(cart, 'qty', 2)"), 1);
+      expect(eval('length(syrups)'), 2);
+      expect(eval("contains(syrups, 'honey')"), true);
+      expect(eval("if(qty > 1, 'yes', 'no')"), 'yes');
+      expect(eval('isEmpty(cart)'), false);
+      expect(eval("number('4.5') + 1"), 5.5);
+      expect(eval("where(cart, 'qty', 2)"), [
+        {'name': 'Oat latte', 'qty': 2, 'total': 12.9},
+      ]);
+      expect(eval("length(where(cart, 'qty'))"), 2);
+      expect(eval("without(syrups, ['honey'])"), ['vanilla']);
+    });
+
+    test('member access', () {
+      expect(eval('cart[1].name'), 'Oat latte');
+      expect(eval('cart[qty - 1].total'), 12.9);
+      expect(eval('cart.length'), 2);
+      expect(eval('syrups[5]'), isNull);
+    });
+
+    test('invalid expressions evaluate to null', () {
+      expect(eval('1 +'), isNull);
+      expect(eval('nope(1)'), isNull);
+      expect(eval("'open"), isNull);
+    });
+
+    test('substitute and stringify', () {
+      expect(
+        FormulaEvaluator.substitute(r'Total ${= money(qty * price)}!', resolve),
+        r'Total $10.50!',
+      );
+      expect(FormulaEvaluator.substitute(r'${= 0.1 + 0.2}', resolve), '0.3');
+      expect(FormulaEvaluator.substitute(r'${= 3 * 2.0}', resolve), '6');
+      expect(
+        FormulaEvaluator.substitute(r"${= qty > 1 ? '}' : '{'}", resolve),
+        '}',
+      );
+      expect(FormulaEvaluator.substitute(r'\${= 1}', resolve), r'\${= 1}');
+      expect(FormulaEvaluator.exactExpression(r' ${= a + b} '), ' a + b');
+      expect(FormulaEvaluator.exactExpression(r'${= a} and ${b}'), isNull);
+    });
+
+    test('referenced paths', () {
+      expect(
+        FormulaEvaluator.referencedPaths(
+          "money(sum(storage.cart, 'total')) + item.name + cart[index].qty",
+        ),
+        {'storage.cart', 'item.name', 'cart', 'index'},
+      );
+      expect(
+        FormulaEvaluator.referencedPathsInText(r'${= a + 1} ${b} ${= c}'),
+        {'a', 'c'},
+      );
+    });
+  });
+
+  testWidgets('formulas read variables through PropertyValueDelegate', (
+    tester,
+  ) async {
+    final List<VariableData> variables = [
+      VariableData(
+        id: 'qty',
+        name: 'qty',
+        type: VariableType.integer,
+        value: 2,
+      ),
+      VariableData(
+        id: 'lines',
+        name: 'lines',
+        type: VariableType.list,
+        value: [
+          {'total': 8.6},
+          {'total': 11.85},
+        ],
+      ),
+    ];
+    late ScopedValues values;
+    await tester.pumpWidget(
+      IndexedItemProvider(
+        item: IndexedItem(0, {'price': 4.25, 'name': 'Cortado'}),
+        child: Builder(
+          builder: (context) {
+            values = ScopedValues.of(context, variablesOverrides: variables);
+            return const SizedBox();
+          },
+        ),
+      ),
+    );
+
+    String sub(String text) => PropertyValueDelegate.substituteVariables(
+      text,
+      scopedValues: values,
+      nullSubstitutionMode: NullSubstitutionMode.emptyString,
+    );
+
+    expect(sub(r'${qty} × ${= money(item.price * qty)}'), r'2 × $8.50');
+    expect(sub(r"${= sum(lines, 'total')}"), '20.45');
+    expect(sub(r'${= lines.length} ${item.name}'), '2 Cortado');
+    expect(
+      PropertyValueDelegate.getVariableValueFromPath<num>(
+        r'${= qty * 3}',
+        scopedValues: values,
+      ),
+      6,
+    );
+    expect(
+      PropertyValueDelegate.getVariableValueFromPath<bool>(
+        r'${= qty > 1}',
+        scopedValues: values,
+      ),
+      true,
+    );
+    expect(
+      FunctionsRepository.substituteNewValue(
+        r'[{"name": "${item.name}", "unit": "${= item.price * qty}"}]',
+        VariableType.list,
+        values,
+      ),
+      '[{"name":"Cortado","unit":8.5}]',
+    );
+    expect(
+      FunctionsRepository.substituteNewValue(
+        r'${= item}',
+        VariableType.map,
+        values,
+      ),
+      '{"price":4.25,"name":"Cortado"}',
+    );
+    expect(
+      PropertyValueDelegate.substituteVariablesInJson(
+        r'{"total": "${= item.price * qty}", "label": "${= item.name} x${qty}"}',
+        scopedValues: values,
+      ),
+      {'total': 8.5, 'label': 'Cortado x2'},
+    );
+  });
+}
diff --git a/test/semantics_test.dart b/test/semantics_test.dart
new file mode 100644
index 00000000..e9432117
--- /dev/null
+++ b/test/semantics_test.dart
@@ -0,0 +1,78 @@
+import 'package:codelessly_api/codelessly_api.dart';
+import 'package:codelessly_sdk/codelessly_sdk.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:provider/provider.dart';
+
+RectangleNode tappable(String id, String name) => RectangleNode(
+  id: id,
+  name: name,
+  basicBoxLocal: NodeBox(0, 0, 40, 40),
+  reactions: [
+    Reaction(
+      action: LinkAction(url: ''),
+      trigger: TriggerModel(type: TriggerType.click),
+    ),
+  ],
+)..parentID = kRootNode;
+
+Future<void> pumpNode(WidgetTester tester, BaseNode node) async {
+  final registry = NodeRegistry()..setNodes({node.id: node});
+  final manager = PassiveNodeTransformerManager(
+    registry.getNodeByID,
+    (context, bounds, pageID, layoutID, canvasID) => const SizedBox(),
+  );
+  await tester.pumpWidget(
+    ChangeNotifierProvider<CodelesslyContext>.value(
+      value: CodelesslyContext.empty(),
+      child: MaterialApp(
+        home: Align(
+          alignment: Alignment.topLeft,
+          child: Builder(
+            builder: (context) => manager.buildWidgetFromNode(
+              node,
+              context,
+              settings: const WidgetBuildSettings(debugLabel: 'test'),
+            ),
+          ),
+        ),
+      ),
+    ),
+  );
+}
+
+void main() {
+  testWidgets('a tappable node without text reads as a named button', (
+    tester,
+  ) async {
+    final SemanticsHandle handle = tester.ensureSemantics();
+    await pumpNode(tester, tappable('back', 'Back to menu'));
+
+    expect(
+      tester.getSemantics(find.bySemanticsLabel('Back to menu')),
+      matchesSemantics(
+        label: 'Back to menu',
+        isButton: true,
+        hasTapAction: true,
+      ),
+    );
+    handle.dispose();
+  });
+
+  test('a default node name is not used as a label', () {
+    expect(
+      WidgetNodeTransformerManager.semanticLabelFor(
+        tappable('r', 'Rectangle 2'),
+        const [],
+      ),
+      '',
+    );
+    expect(
+      WidgetNodeTransformerManager.semanticLabelFor(
+        tappable('r', 'Add to bag'),
+        const [],
+      ),
+      'Add to bag',
+    );
+  });
+}
diff --git a/test/style_overrides_test.dart b/test/style_overrides_test.dart
new file mode 100644
index 00000000..67fe0c8e
--- /dev/null
+++ b/test/style_overrides_test.dart
@@ -0,0 +1,88 @@
+import 'package:codelessly_api/codelessly_api.dart';
+import 'package:codelessly_sdk/codelessly_sdk.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:provider/provider.dart';
+
+void main() {
+  testWidgets('fill, opacity and size follow bound formulas', (tester) async {
+    final RectangleNode node = RectangleNode.fromJson({
+      ...RectangleNode(
+        id: 'cup',
+        name: 'Cup layer',
+        basicBoxLocal: NodeBox(0, 0, 40, 40),
+        fills: [
+          PaintModel.solid(id: 'fill', color: ColorRGB.fromHex('#EDE3D6')),
+        ],
+      ).toJson(),
+      'variables': {
+        'fill': r"${= qty > 1 ? '#C8643B' : '#EDE3D6'}",
+        'height': r'${= qty * 20}',
+        'opacity': r'${= qty > 2 ? 0.5 : 1}',
+      },
+    });
+    node.parentID = kRootNode;
+    final registry = NodeRegistry()..setNodes({node.id: node});
+    final manager = PassiveNodeTransformerManager(
+      registry.getNodeByID,
+      (context, bounds, pageID, layoutID, canvasID) => const SizedBox(),
+    );
+    final Observable<VariableData> qty = Observable(
+      VariableData(
+        id: 'qty',
+        name: 'qty',
+        type: VariableType.integer,
+        value: 1,
+      ),
+    );
+    final CodelesslyContext codelesslyContext = CodelesslyContext.empty()
+      ..variables['qty'] = qty;
+
+    await tester.pumpWidget(
+      ChangeNotifierProvider<CodelesslyContext>.value(
+        value: codelesslyContext,
+        child: MaterialApp(
+          home: Align(
+            alignment: Alignment.topLeft,
+            child: Builder(
+              builder: (context) => manager.buildWidgetFromNode(
+                node,
+                context,
+                settings: const WidgetBuildSettings(debugLabel: 'test'),
+              ),
+            ),
+          ),
+        ),
+      ),
+    );
+
+    Color? color() => tester.allWidgets
+        .map(
+          (w) => switch (w) {
+            final Ink ink => ink.decoration,
+            final DecoratedBox box => box.decoration,
+            _ => null,
+          },
+        )
+        .whereType<BoxDecoration>()
+        .map((decoration) => decoration.color)
+        .nonNulls
+        .firstOrNull;
+    final Finder box = find.byWidgetPredicate(
+      (w) => w is Container && w.decoration is BoxDecoration,
+    );
+
+    expect(tester.getSize(box).height, 20);
+    expect(color(), const Color(0xFFEDE3D6));
+    expect(find.byType(Opacity), findsNothing);
+
+    qty.set(qty.value.copyWith(value: 3));
+    await tester.pump();
+
+    expect(tester.getSize(box).height, 60);
+    expect(color(), const Color(0xFFC8643B));
+    expect(tester.widget<Opacity>(find.byType(Opacity)).opacity, 0.5);
+    // The node itself is unchanged.
+    expect(node.basicBoxLocal.height, 40);
+  });
+}
diff --git a/test/toast_test.dart b/test/toast_test.dart
new file mode 100644
index 00000000..940850e8
--- /dev/null
+++ b/test/toast_test.dart
@@ -0,0 +1,68 @@
+import 'package:codelessly_api/codelessly_api.dart';
+import 'package:codelessly_sdk/codelessly_sdk.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:provider/provider.dart';
+
+void main() {
+  testWidgets('showToast shows the message with variables, then hides it', (
+    tester,
+  ) async {
+    late BuildContext context;
+    final ctx = CodelesslyContext.empty()
+      ..variables['drink'] = Observable(
+        VariableData(id: 'drink', name: 'drink', value: 'Cortado'),
+      );
+    await tester.pumpWidget(
+      ChangeNotifierProvider<CodelesslyContext>.value(
+        value: ctx,
+        child: MaterialApp(
+          home: Builder(
+            builder: (c) {
+              context = c;
+              return const SizedBox();
+            },
+          ),
+        ),
+      ),
+    );
+
+    final reactions = [
+      Reaction(
+        action: ShowToastAction(
+          message: r'Added ${drink} to your order',
+          duration: 1000,
+        ),
+        trigger: TriggerModel(type: TriggerType.click),
+      ),
+    ];
+    FunctionsRepository.triggerAction(
+      context,
+      TriggerType.click,
+      reactions: reactions,
+    );
+    await tester.pump();
+    await tester.pump(const Duration(milliseconds: 300));
+    expect(find.text('Added Cortado to your order'), findsOneWidget);
+
+    // A second toast replaces the first.
+    FunctionsRepository.triggerAction(
+      context,
+      TriggerType.click,
+      reactions: [
+        Reaction(
+          action: ShowToastAction(message: 'Second', duration: 500),
+          trigger: TriggerModel(type: TriggerType.click),
+        ),
+      ],
+    );
+    await tester.pump();
+    expect(find.text('Added Cortado to your order'), findsNothing);
+    expect(find.text('Second'), findsOneWidget);
+
+    await tester.pump(const Duration(milliseconds: 800));
+    await tester.pump();
+    await tester.pump(const Duration(milliseconds: 300));
+    expect(find.text('Second'), findsNothing);
+  });
+}