Expressions

Syntax Forms

• $draft.title reads a runtime value and creates a writable binding for controls that support bindings.
• ${draft.title} evaluates a typed expression and returns the expression result.
• /requests/${params.request} interpolates expression results inside a string parameter.
• Plain text stays literal unless it is a dotted runtime path, a $ reference, or contains${...} interpolation.

xml
<TextInput label="Task title" value="$draft.title" />
<Text count="${tasks.length}" i18n="tasks.count" />
<Link to="/requests/${params.request}" i18n="requests.open" />

Runtime Scope

Expressions can read values exposed by setup nodes, route params, and loop scopes.

• State values are reactive local page objects, such as draft.title.
• Query values are JSON responses stored under their query id, such as tasks.length.
• For exposes the item alias and index inside the loop body.
• Dynamic page files expose route parameters through params.

xml
<Query id="tasks" path="/api/tasks" />
<For each="$tasks" as="task">
  <Text i18n="tasks.row" values="${{ index: index + 1, title: task.title }}" />
</For>

Operators

Supported operators cover page conditions, derived values, and request payloads.

• Arithmetic: +, -, *, /, %, and **.
• Equality and comparison: ===, !==, ==, !=, <, <=, >, and >=.
• Logical expressions: &&, ||, ??, and !.
• Membership: status in ['open', 'pending'] checks strings, arrays, and object keys.
• Conditional values: condition ? yes : no.
• Optional chaining: user?.profile?.name.

xml
<Button isDisabled="${!draft.title || saving}" i18n="tasks.create" />
<Text if="${task.status === 'open'}" i18n="tasks.title" values="${{ title: task.title }}" />
<Badge label="${task.priority >= 5 ? 'High' : 'Normal'}" />
<Text i18n="tasks.owner" values="${{ name: task.owner?.name ?? 'Unassigned' }}" />

Arrays, Objects, and Templates

Wrapped expressions preserve typed values, so arrays and objects can be sent directly to actions.

xml
<Action
  action="/api/tasks"
  invalidate="${['tasks']}"
  json="${{ title: draft.title, priority: Number(draft.priority) }}"
>
  <Button i18n="tasks.create" />
</Action>
​
<Text i18n="tasks.summary" values="${{ summary: `Task ${task.id}: ${task.title}` }}" />

Safe Calls

Only whitelisted global helpers can be called from expressions.

• Type helpers: String(value), Number(value), and Boolean(value).
• Array helper: Array.isArray(value).
• Math helpers: Math.abs, Math.ceil, Math.floor, Math.max, Math.min, Math.round, and Math.trunc.

xml
<Text i18n="tasks.id" values="${{ id: String(task.id) }}" />
<Text if="${Array.isArray(tasks) &amp;&amp; tasks.length > 0}" i18n="tasks.ready" />
<Text i18n="tasks.total" values="${{ total: Math.round(total) }}" />

Bindings

Writable form bindings use the $ reference form. A typed expression can read a state field, but it does not create a writable control binding.

xml
<State id="draft" title="" />
​
<!-- writable -->
<TextInput label="Task title" value="$draft.title" />
​
<!-- read-only expression result -->
<Text i18n="tasks.draftTitle" values="${{ title: draft.title || 'Untitled' }}" />

XML Escaping

XML attributes must still be valid XML. Escape reserved characters before the expression reaches the LongLink evaluator.

• Use < for less-than comparisons.
• Use && for logical and.
• Quote XML attributes with single quotes when the expression contains many double quotes.

xml
<Text if="${amount &lt; 100}" i18n="orders.small" />
<Text if="${ready &amp;&amp; tasks.length > 0}" i18n="tasks.ready" />

Unsupported Syntax

Expressions are intentionally read-only and sandboxed.

• Arbitrary function calls and object method calls are blocked.
• Assignments, updates, constructors, classes, imports, and dynamic code execution are blocked.
• Inherited properties and unsafe prototype names are not readable.

xml
<!-- blocked -->
<Text i18n="tasks.title" values="${{ title: task.title.toUpperCase() }}" />
<Text i18n="tasks.created" values="${{ created: new Date() }}" />
<Text i18n="tasks.unsafe" values="${{ unsafe: task.__proto__ }}" />