Rich Content and Expressions

This page documents two core ABL capabilities: rich content output formats (voice, cards, carousels, interactive actions, templates) and the expression language (operators, functions, template interpolation).

Rich Content

ABL supports multi-format output for delivering responses across different channels (web, mobile, voice, messaging platforms). The VOICE:, RICH_CONTENT:, and ACTIONS: blocks can be attached to any RESPOND statement, COMPLETE condition, or lifecycle handler.

Overview

A single response can include:

Plain text — the default RESPOND string.
Voice configuration — SSML markup or natural language voice instructions.
Rich content — Markdown, Adaptive Cards, HTML, Slack Block Kit, WhatsApp, or AG-UI.
Carousels — scrollable card collections with images and buttons.
Interactive actions — buttons, select menus, and input fields.
Templates — reusable named response definitions with interpolation.

The runtime selects the appropriate format based on the delivery channel.

Voice configuration

Voice configuration provides channel-specific voice output. The VOICE: block can appear alongside any RESPOND.

Syntax

RESPOND: "Your booking is confirmed for December 15th."
VOICE:
  ssml: |
    <speak>
      Your booking is confirmed for <say-as interpret-as="date" format="mdy">12/15/2025</say-as>.
    </speak>
  instructions: "Speak in a warm, congratulatory tone"
  plain_text: "Your booking is confirmed for December fifteenth."

Voice properties

Property	Type	Required	Default	Description
`ssml`	`string`	No	—	W3C SSML markup for TTS engines (Google, Azure, Amazon Polly).
`instructions`	`string`	No	—	Natural language voice style instructions (OpenAI Realtime, Gemini Live).
`plain_text`	`string`	No	—	Voice-optimized plaintext. Used by ElevenLabs and as a fallback for all engines.

SSML example

VOICE:
  ssml: |
    <speak>
      <prosody rate="slow" pitch="+2st">
        Your wire transfer of <say-as interpret-as="currency">$50,000 USD</say-as>
        has been executed.
      </prosody>
      <break time="500ms"/>
      The confirmation number is
      <say-as interpret-as="characters">WR-2024-88431</say-as>.
    </speak>

Natural language instructions

For voice platforms that accept style instructions rather than SSML:

VOICE:
  instructions: "Speak slowly and clearly, emphasizing the confirmation number. Use a professional but warm tone."

Rich content formats

The rich-content block provides format-specific variants of a response. The runtime selects the variant matching the delivery channel.

In the .agent.abl format the block keyword is FORMATS:. The .agent.yaml format accepts rich_content: or formats:. (RICH_CONTENT: is a legacy alias accepted only in flow-step overrides.)

Syntax

RESPOND: "Here are your flight options."
FORMATS:
  MARKDOWN: |
    ## Flight Options
    | Flight | Departure | Arrival | Price |
    |--------|-----------|---------|-------|
    | AA 142 | 8:00 AM   | 11:30 AM | $349 |
    | UA 891 | 10:15 AM  | 1:45 PM  | $289 |

  ADAPTIVE_CARD: |
    {
      "type": "AdaptiveCard",
      "body": [
        {"type": "TextBlock", "text": "Flight Options", "size": "large"}
      ]
    }

  HTML: |
    <div class="flight-results">
      <h2>Flight Options</h2>
      <table>...</table>
    </div>

  SLACK: |
    {
      "blocks": [
        {"type": "header", "text": {"type": "plain_text", "text": "Flight Options"}}
      ]
    }

Rich content properties

Channel-specific string formats:

Property	Type	Required	Default	Description
`MARKDOWN`	`string`	No	—	Formatted markdown text.
`ADAPTIVE_CARD`	`string`	No	—	JSON string conforming to the Microsoft Adaptive Cards schema.
`HTML`	`string`	No	—	HTML content for web-based channels.
`SLACK`	`string`	No	—	JSON string conforming to the Slack Block Kit format.
`AG_UI`	`string`	No	—	JSON string for AG-UI / CopilotKit events.
`WHATSAPP`	`string`	No	—	JSON string for WhatsApp interactive messages.

Structured template formats (channel-neutral; the runtime renders them per channel):

Property	Type	Description
`CAROUSEL`	`object`	Scrollable card collection. See Carousels.
`QUICK_REPLIES`	`array`	Quick-reply chips: each `{ id, label, iconUrl? }`.
`LIST`	`object`	`{ title?, items: [{ title, subtitle?, imageUrl?, defaultActionUrl? }] }`.
`IMAGE`	`object`	`{ url, alt?, thumbnailUrl?, caption? }`.
`VIDEO`	`object`	`{ url, alt?, thumbnailUrl?, caption? }`.
`AUDIO`	`object`	`{ url, alt?, thumbnailUrl?, caption? }`.
`FILE`	`object`	`{ url, filename, sizeBytes?, mimeType? }`.
`KPI`	`object`	`{ label, value, unit?, trend?: up/down/flat, iconUrl? }`.
`TABLE`	`object`	`{ columns: [{ key, header, align?: left/center/right }], rows, maxVisibleRows? }`.
`CHART`	`object`	`{ type: bar/line/pie, title?, data: [{ label, value, color? }] }`.
`FORM`	`object`	`{ title?, fields: [ActionElement], submitLabel? }`.
`PROGRESS`	`object`	`{ label?, value, max?, variant?: bar/circle }`.
`FEEDBACK`	`object`	`{ prompt, type: thumbs/stars/scale, max? }`.

Named templates (in the TEMPLATES: block) may also declare a RENDERABLES: list — customer-owned structured payloads with name, payload, optional targets (api/sdk_websocket/http_async), fallbackText, and schemaRef. Data-rich templates (KPI, TABLE, CHART, LIST, CAROUSEL, …) also support collection binding via from: / template: to render one entry per array item.

Carousels

Carousels display a horizontal scrollable collection of cards, each with a title, subtitle, image, and action buttons.

Syntax

FORMATS:
  CAROUSEL:
    - title: "Economy Class"
      subtitle: "$289 - UA 891"
      imageUrl: "https://cdn.example.com/economy.jpg"
      defaultActionUrl: "https://booking.example.com/ua891"
      buttons:
        - id: select_economy
          type: button
          label: "Select"
          value: "ua891_economy"

    - title: "Business Class"
      subtitle: "$1,249 - UA 891"
      imageUrl: "https://cdn.example.com/business.jpg"
      buttons:
        - id: select_business
          type: button
          label: "Select"
          value: "ua891_business"

Carousel card properties

Property	Type	Required	Default	Description
`title`	`string`	Yes	—	Card title.
`subtitle`	`string`	No	—	Card subtitle or description.
`imageUrl`	`string`	No	—	URL for the card image.
`defaultActionUrl`	`string`	No	—	URL opened when the card itself is tapped.
`buttons`	`array`	No	—	Action buttons. See Interactive actions.

Interactive actions

Interactive actions add buttons, select menus, and input fields to a response. Users interact with these elements, and the agent handles the interactions via ON_ACTION blocks.

Syntax

RESPOND: "How would you like to proceed?"
ACTIONS:
  - id: confirm_wire
    type: button
    label: "Confirm Wire"
    value: "confirmed"

  - id: modify_amount
    type: button
    label: "Modify Amount"
    value: "modify"

  - id: cancel
    type: button
    label: "Cancel"
    value: "cancelled"

Action element properties

Property	Type	Required	Default	Description
`id`	`string`	Yes	—	Unique action identifier. Referenced in `ON_ACTION` handlers.
`type`	`string`	Yes	—	Element type: `button`, `select`, or `input`.
`label`	`string`	Yes	—	Display label.
`value`	`string`	No	—	Hidden value sent when the user interacts with this element.
`description`	`string`	No	—	Subtitle or help text (for list items).
`options`	`array`	No	—	Options for `select` type. Each has `id`, `label`, `description`.
`inputType`	`string`	No	—	Input type for `input` elements: `text`, `number`, `date`, `time`, `email`.
`placeholder`	`string`	No	—	Placeholder text for `input` elements.
`required`	`boolean`	No	—	Whether the input is required before submission.

Select element example

ACTIONS:
  - id: select_account
    type: select
    label: "Choose Account"
    options:
      - id: checking
        label: "Checking ****4521"
        description: "Available: $12,340.50"
      - id: savings
        label: "Savings ****8872"
        description: "Available: $45,200.00"

Input element example

ACTIONS:
  - id: amount_input
    type: input
    label: "Transfer Amount"
    inputType: number
    placeholder: "Enter amount"
    required: true

  - id: reference_input
    type: input
    label: "Reference (optional)"
    inputType: text
    placeholder: "Invoice number, memo, etc."
    required: false
  submitLabel: "Submit"
  submitId: "submit_transfer"

Form submission

When the ACTIONS block contains input elements, you can specify a submitLabel and submitId for the form submission button:

Property	Type	Required	Default	Description
`submitLabel`	`string`	No	—	Label for the form submit button.
`submitId`	`string`	No	—	Action ID emitted when the form is submitted.

ON_ACTION handlers

Handle user interactions with action elements in flow steps:

FLOW:
  review_wire:
    RESPOND: "Ready to proceed?"
    ACTIONS:
      - id: confirm
        type: button
        label: "Confirm"
      - id: cancel
        type: button
        label: "Cancel"
    ON_ACTION:
      confirm:
        DO:
          - SET: user_confirmed = true
          - RESPOND: "Executing your wire transfer."
            FORMATS:
              MARKDOWN: "**Executing your wire transfer.**"
          - GOTO: execute_wire_step
      cancel:
        RESPOND: "Wire transfer cancelled."
        GOTO: cleanup

The ON_ACTION handler properties are described below.

Property	Type	Required	Default	Description
`ACTION_ID`	`string`	Yes	—	Which action element triggered this handler.
`CONDITION`	`string`	No	—	Optional condition based on the action value.
`DO`	ordered action list	No	—	Preferred form when order or nested rich `FORMATS:` matters.
`RESPOND`	`string`	No	—	Response message; supports nested `FORMATS:` inside a `DO` action.
`SET`	`Record<string,string>`	No	—	Variable assignments.
`CLEAR`	`string[]`	No	—	Session variables to clear.
`CALL`	`string`	No	—	Tool call; use `AS result_key` to store the result.
`GOTO` / `TRANSITION` / `THEN`	`string`	No	—	Flow step to transition to.
`HANDOFF`	`string`	No	—	Declared handoff target agent.
`DELEGATE`	`string`	No	—	Declared delegate target agent; supports nested `RETURN` and `ON_RETURN`.
`COMPLETE`	`boolean`	No	`true`	Complete the current flow.

If a handler RESPOND includes rich FORMATS: before terminal routing, that payload is forwarded as the fallback final channel payload. The terminal target’s own rich payload takes precedence.

Templates

Templates are named, reusable response definitions declared in the TEMPLATES: block. They support {{}} interpolation and multi-format variants.

Syntax

TEMPLATES:
  wire_confirmation:
    DEFAULT: |
      **Wire Confirmation -- {{confirmation_number}}**
      From: ****{{source_last4}} | To: {{beneficiary_name}}
      Amount: {{amount}} {{currency}} | Fees: {{fees}} | Total: {{total_debit}}
      Status: {{status}} | ETA: {{estimated_arrival}}
    MARKDOWN: |
      ## Wire Transfer Confirmation
      | Field | Value |
      |-------|-------|
      | Confirmation | {{confirmation_number}} |
      | Amount | {{amount}} {{currency}} |
      | Status | {{status}} |

  fee_breakdown:
    DEFAULT: |
      **Fee Breakdown for {{transfer_type}} wire**
      Wire fee: {{wire_fee}} {{currency}}
      {{#if intermediary_fee}}Intermediary fee: {{intermediary_fee}} {{currency}}{{/if}}
      **Total fees: {{total_fees}} {{currency}}**

Template properties

Property	Type	Required	Default	Description
`name`	`string`	Yes	—	Template name (the YAML key). Referenced via `TEMPLATE(name)`.
`DEFAULT`	`string`	Yes	—	Default template body with `{{}}` interpolation.
`MARKDOWN`	`string`	No	—	Markdown variant.
`ADAPTIVE_CARD`	`string`	No	—	Adaptive Card JSON variant.
`ACTIONS`	`object`	No	—	Interactive actions attached to this template.

Referencing templates

Use TEMPLATE(name) in any RESPOND value:

RESPOND: TEMPLATE(wire_confirmation)

Template interpolation

Templates use {{variable_name}} for value substitution and {{#if variable}}...{{/if}} for conditional sections:

DEFAULT: |
  Hello, {{customer_name}}.
  {{#if has_loyalty}}Your loyalty tier: {{loyalty_tier}}.{{/if}}
  How can I help you today?

Channel selection

The runtime selects the response format based on the delivery channel:

Channel	Priority format	Fallback
Web/SDK	`RICH_CONTENT` (Markdown, HTML, AG-UI)	Plain text
Mobile	`RICH_CONTENT` (Adaptive Card, Carousel)	Plain text
Voice	`VOICE` (SSML, instructions, plain_text)	RESPOND text
Slack	`RICH_CONTENT` (SLACK)	Markdown
WhatsApp	`RICH_CONTENT` (WHATSAPP)	Plain text

If the preferred format is not available, the runtime falls back through the priority chain until it finds a defined format. Plain text (RESPOND) is always the final fallback.

Expressions and Functions

ABL expressions are used in conditions (WHEN, CHECK, constraint rules), value assignments (SET), template interpolation ({{}}), and function calls. This section documents the expression syntax and all 36 built-in functions.

Expression syntax

Comparison operators

Operator	Syntax	Description
`==`	`a == b`	Equal to.
`!=`	`a != b`	Not equal to.
`>`	`a > b`	Greater than.
`<`	`a < b`	Less than.
`>=`	`a >= b`	Greater than or equal to.
`<=`	`a <= b`	Less than or equal to.
`in`	`a IN [x,y,z]`	Value is in the list.
`not_in`	`a NOT IN [x]`	Value is not in the list.
`matches`	`a matches r`	Value matches a regular expression.
`contains`	`a contains b`	String contains substring, or array contains element.
`startsWith`	`a startsWith b`	String starts with a prefix.
`endsWith`	`a endsWith b`	String ends with a suffix.

Logical operators

Operator	Syntax	Description
`AND`	`a AND b`	Both conditions must be true.
`OR`	`a OR b`	At least one must be true.
`NOT`	`NOT a`	Negates the condition.

Write logical operators in uppercase (AND, OR, NOT). ! is also accepted as a prefix negation.

Unary operators

Operator	Syntax	Description
`NOT` / `!`	`NOT condition` / `!condition`	Negates a condition.
`IS SET`	`var IS SET`	True if the variable is not null/undefined (empty string counts as set).
`IS NOT SET`	`var IS NOT SET`	True if the variable is null or undefined.
`is_number`	`var is_number`	True if the variable is a number.

Operator precedence

Parentheses ()
Unary operators (NOT, IS SET, IS NOT SET)
Comparison operators (==, !=, >, <, >=, <=, contains, matches)
AND
OR

Use parentheses to override default precedence:

WHEN: (status == "active" OR status == "pending") AND amount > 0

Variable paths and dot notation

Reference variables using dot notation to access nested values:

user.name                  # Access nested property
user.addresses[0].city     # Array index access
acctResult.status          # Tool result field

Path resolution rules

The evaluator looks up the full path in the session context.
The Platform resolves each segment left to right: user.address.city resolves user, then address on the result, then city.
If any segment resolves to null or undefined, the entire path resolves to undefined.
Array access uses bracket notation: items[0], items[2].name.

Template strings

Template strings use {{}} syntax for variable interpolation within RESPOND, summary, and other string properties:

RESPOND: "Hello, {{customer_name}}! Your balance is {{available_balance}}."

Conditional sections

Templates support conditional rendering with {{#if}}...{{/if}}:

RESPOND: |
  Transfer complete.
  {{#if fx_rate}}Exchange rate: {{fx_rate}}{{/if}}
  Estimated arrival: {{estimated_arrival}}.

Function calls in templates

You can call built-in functions within template strings:

SET:
  formatted_balance = FORMAT_CURRENCY(available_balance, "USD")
RESPOND: "Your balance is {{formatted_balance}}."

Built-in function reference

ABL provides 36 built-in functions organized into seven categories. All functions are called with FUNCTION_NAME(arg1, arg2, ...) syntax. Function names are uppercase.

Math functions

| Function | Signature | Description | Example | | -------- | ------------------------------- | ---------------------------------------------- | --------------------------------------------------- | ------------------------ | | ADD | ADD(a, b) -> number | Add two numbers. | ADD(2, 3) returns 5 | | SUB | SUB(a, b) -> number | Subtract b from a. | SUB(10, 3) returns 7 | | MUL | MUL(a, b) -> number | Multiply two numbers. | MUL(4, 5) returns 20 | | DIV | DIV(a, b) -> number | null | Divide a by b. Returns null for division by zero. | DIV(10, 2) returns 5 | | ROUND | ROUND(n, decimals?) -> number | Round to specified decimal places. Default: 0. | ROUND(3.14159, 2) returns 3.14 | | ABS | ABS(n) -> number | Absolute value. | ABS(-5) returns 5 | | MIN | MIN(a, b) -> number | Return the smaller of two numbers. | MIN(3, 7) returns 3 | | MAX | MAX(a, b) -> number | Return the larger of two numbers. | MAX(3, 7) returns 7 | Math functions coerce string arguments to numbers automatically: ADD("2", "3") returns 5.

String functions

Function	Signature	Description	Example
`UPPER`	`UPPER(s) -> string`	Convert to uppercase.	`UPPER("hello")` returns `"HELLO"`
`LOWER`	`LOWER(s) -> string`	Convert to lowercase.	`LOWER("HELLO")` returns `"hello"`
`TRIM`	`TRIM(s) -> string`	Strip leading/trailing whitespace.	`TRIM(" hi ")` returns `"hi"`
`SUBSTRING`	`SUBSTRING(s, start, end?) -> string`	Extract a substring.	`SUBSTRING("hello", 0, 3)` returns `"hel"`
`REPLACE`	`REPLACE(s, find, repl) -> string`	Replace all occurrences.	`REPLACE("a,b,c", ",", "-")` returns `"a-b-c"`
`SPLIT`	`SPLIT(s, delimiter) -> string[]`	Split string into array.	`SPLIT("a,b,c", ",")` returns `["a","b","c"]`
`JOIN`	`JOIN(arr, delimiter) -> string`	Join array into string.	`JOIN(["a","b"], ", ")` returns `"a, b"`
`PAD_START`	`PAD_START(s, length, char?) -> string`	Left-pad to specified length.	`PAD_START("42", 6, "0")` returns `"000042"`
`PAD_END`	`PAD_END(s, length, char?) -> string`	Right-pad to specified length.	`PAD_END("42", 6, "0")` returns `"420000"`
`REPEAT`	`REPEAT(s, count) -> string`	Repeat string N times.	`REPEAT("", 4)` returns `"***"`

The string functions gracefully handle null and undefined and return an empty string: UPPER(null) returns "". To prevent memory issues, the limit on string output is 100,000 characters.

Formatting functions

Function	Signature	Description	Example
`MASK`	`MASK(s, pattern, char?) -> string`	Mask a string. See Mask Patterns below.	`MASK("4111111111111111", "last4")` returns `"************1111"`
`FORMAT_CURRENCY`	`FORMAT_CURRENCY(n, currency, locale?) -> string`	Format a number as currency.	`FORMAT_CURRENCY(1234.5, "USD")` returns `"$1,234.50"`
`FORMAT_DATE`	`FORMAT_DATE(d, format, tz?) -> string`	Format a date string.	`FORMAT_DATE("2024-03-15T10:30:00Z", "YYYY-MM-DD")` returns `"2024-03-15"`
`ORDINAL`	`ORDINAL(n) -> string`	Convert number to ordinal string.	`ORDINAL(1)` returns `"1st"`, `ORDINAL(22)` returns `"22nd"`

The mask patterns are explained below.

Pattern	Behavior	Example result
`last4`	Mask all characters except the last 4.	`"************1111"`
`first4`	Mask all characters except the first 4.	`"4111************"`
`N*N`	Show N chars at start, mask middle, show N at end.	`MASK(s, "4*4")` shows 4+4

The default mask character is *. Pass a third argument to use a different character: MASK(ssn, "last4", "x"). The date format uses the following notations:

Token	Description	Example
`YYYY`	Four-digit year	`2024`
`MM`	Two-digit month	`03`
`DD`	Two-digit day	`15`
`HH`	Two-digit hour (24h)	`10`
`mm`	Two-digit minute	`30`
`ss`	Two-digit second	`00`

Example: FORMAT_DATE("2024-03-15T10:30:00Z", "YYYY-MM-DD HH:mm") returns "2024-03-15 10:30".

Type checking and coercion functions

Function	Signature	Description	Example
`IS_ARRAY`	`IS_ARRAY(x) -> boolean`	True if the value is an array.	`IS_ARRAY([1,2])` returns `true`
`IS_NUMBER`	`IS_NUMBER(x) -> boolean`	True if the value is a number (not NaN).	`IS_NUMBER(42)` returns `true`
`IS_STRING`	`IS_STRING(x) -> boolean`	True if the value is a string.	`IS_STRING("hi")` returns `true`
`TO_NUMBER`	`TO_NUMBER(x) -> number`	null	Convert to number. Returns `null` if conversion fails. `TO_NUMBER("42")` returns `42`
`TO_STRING`	`TO_STRING(x) -> string`	Convert to string. Returns `""` for null/undefined.	`TO_STRING(42)` returns `"42"`

Array functions

Function	Signature	Description	Example
`LENGTH`	`LENGTH(x) -> number`	Array length or string length. Returns 0 for other types.	`LENGTH([1,2,3])` returns `3`
`ARRAY_FIND`	`ARRAY_FIND(arr, field, value) -> object`	null	Find first element where `field == value`. `ARRAY_FIND(users, "id", 42)` returns the matching object
`ARRAY_FIND_INDEX`	`ARRAY_FIND_INDEX(arr, field, value) -> number`	Find index of first match. Returns -1 if not found.	`ARRAY_FIND_INDEX(items, "type", "b")` returns the index

Object functions

Function	Signature	Description	Example
`OBJECT_KEYS`	`OBJECT_KEYS(obj) -> string[]`	Return array of object keys.	`OBJECT_KEYS({a:1, b:2})` returns `["a","b"]`
`OBJECT_VALUES`	`OBJECT_VALUES(obj) -> any[]`	Return array of object values.	`OBJECT_VALUES({a:1, b:2})` returns `[1, 2]`
`OBJECT_MERGE`	`OBJECT_MERGE(obj1, obj2, ...) -> object`	Merge objects. Right-side values win on conflict.	`OBJECT_MERGE({a:1}, {b:2})` returns `{a:1, b:2}`

OBJECT_KEYS and OBJECT_VALUES return an empty array for non-object inputs (null, arrays, strings). OBJECT_MERGE accepts any number of arguments and skips non-object values.

Utility functions

Function	Signature	Description	Example
`COALESCE`	`COALESCE(a, b, ...) -> any`	Return the first non-null, non-undefined value. Returns `null` if all arguments are null.	`COALESCE(null, undefined, "hello")` returns `"hello"`
`NOW`	`NOW() -> string`	Return the current timestamp as an ISO 8601 string.	`NOW()` returns `"2024-03-15T10:30:00.000Z"`
`UNIQUE_ID`	`UNIQUE_ID(length?) -> string`	Generate a random alphanumeric string. Default length: 6.	`UNIQUE_ID(12)` returns `"aB3kM9pQ2xLw"`

COALESCE considers 0 and false as valid (non-null) values: COALESCE(0, "fallback") returns 0. UNIQUE_ID generates a random alphanumeric string suitable for reference numbers. It is not cryptographically secure — do not use it for tokens or secrets.

Content-analysis functions (CEL guardrails)

CEL-based guardrail checks have access to an additional abl.* namespace of content-analysis helpers:

Function	Description
`abl.contains_pii(text)`	True if the text contains PII.
`abl.detect_pii(text)`	Structured PII detection result.
`abl.redact_pii(text)`	Returns the text with PII redacted.
`abl.matches_pattern(text, pattern)`	Regex match (RE2-backed).
`abl.not_matches_pattern(text, pattern)`	Negation of `matches_pattern`.
`abl.word_count(text)`	Word count.
`abl.sentence_count(text)`	Sentence count.
`abl.contains_url(text)`	True if the text contains a URL.
`abl.contains_email(text)`	True if the text contains an email address.
`abl.contains_code(text)`	True if the text contains a fenced code block.

In CEL expressions the core functions above are also available under the abl. namespace with lowercase names (e.g. abl.upper(x)), and CEL-native operators (&&, ||, !, %, in, ternary ? :) and macros (size(), has()) can be used.

Nested function calls

Functions can be nested as arguments to other functions:

SET:
  result = ADD(MUL(2, 3), SUB(10, 4))     # Returns 12
  name = UPPER(TRIM("  hello  "))           # Returns "HELLO"
  fallback = COALESCE(user.lastName, "Guest")

Nesting is limited to a maximum depth of 32 to prevent stack overflow.

Using expressions in ABL

In conditions (WHEN, CHECK, constraint rules)

WHEN: user.age >= 18 AND user.verified == true
CHECK: amount <= available_balance
- REQUIRE sanctions_clear == true

In SET assignments

SET:
  balance_formatted = FORMAT_CURRENCY(available_balance, "USD")
  wire_reference = UNIQUE_ID(12)
  greeting = COALESCE(user.name, "valued customer")

In template interpolation

RESPOND: "Hello, {{customer_name}}! Balance: {{FORMAT_CURRENCY(available_balance, 'USD')}}."

In TRANSFORM pipelines

TRANSFORM:
  SOURCE: search_results
  AS: item
  INTO: filtered_results
  FILTER: item.price <= budget AND item.available == true
  MAP:
    name: item.hotel_name
    price: FORMAT_CURRENCY(item.price, "USD")
  SORT_BY: price ASC
  LIMIT: 5

Type coercion rules

The evaluator applies these coercion rules during expression evaluation:

Context	Rule
Equality (`==`)	null/undefined == null/undefined is true. Strings compared case-sensitively. Numbers parsed from strings.
Inequality (`!=`)	If either side is undefined/null, returns true.
Numeric (`>`, `<`, etc.)	Strings parsed to numbers. Booleans become 0/1. Arrays become length. Undefined becomes 0.
Truthiness (bare variable)	`false`, `0`, `""`, `"false"`, `null`, `undefined`, empty arrays, empty objects are falsy. Everything else is truthy.
IS SET / IS NOT SET	Checks for null/undefined only. Empty string IS SET.

Memory & Constraints — condition expressions in constraint rules, variable paths and session context
Lifecycle & hooks — ON_START and hooks that support rich content
Multi-Agent & Supervisor — COMPLETE conditions with rich responses
Data Types & Utilities — types used in function signatures, lookup validation functions

​Rich Content

​Overview

​Voice configuration

​Syntax

​Voice properties

​SSML example

​Natural language instructions

​Rich content formats

​Syntax

​Rich content properties

​Carousels

​Syntax

​Carousel card properties

​Interactive actions

​Syntax

​Action element properties

​Select element example

​Input element example

​Form submission

​ON_ACTION handlers

​Templates

​Syntax

​Template properties

​Referencing templates

​Template interpolation

​Channel selection

​Expressions and Functions

​Expression syntax

​Comparison operators

​Logical operators

​Unary operators

​Operator precedence

​Variable paths and dot notation

​Path resolution rules

​Template strings

​Conditional sections

​Function calls in templates

​Built-in function reference

​Math functions

​String functions

​Formatting functions

​Type checking and coercion functions

​Array functions

​Object functions

​Utility functions

​Content-analysis functions (CEL guardrails)

​Nested function calls

​Using expressions in ABL

​In conditions (WHEN, CHECK, constraint rules)

​In SET assignments

​In template interpolation

​In TRANSFORM pipelines

​Type coercion rules

​Related pages

Rich Content

Overview

Voice configuration

Syntax

Voice properties

SSML example

Natural language instructions

Rich content formats

Syntax

Rich content properties

Carousels

Syntax

Carousel card properties

Interactive actions

Syntax

Action element properties

Select element example

Input element example

Form submission

ON_ACTION handlers

Templates

Syntax

Template properties

Referencing templates

Template interpolation

Channel selection

Expressions and Functions

Expression syntax

Comparison operators

Logical operators

Unary operators

Operator precedence

Variable paths and dot notation

Path resolution rules

Template strings

Conditional sections

Function calls in templates

Built-in function reference

Math functions

String functions

Formatting functions

Type checking and coercion functions

Array functions

Object functions

Utility functions

Content-analysis functions (CEL guardrails)

Nested function calls

Using expressions in ABL

In conditions (WHEN, CHECK, constraint rules)

In SET assignments

In template interpolation

In TRANSFORM pipelines

Type coercion rules

Related pages