/**
 * Rx — Reactive expression builder.
 *
 * Builds template expressions like "{{ count + 1 }}" or "{{ user.name }}"
 * that are evaluated client-side by the prefab renderer.
 *
 * Usage:
 *   rx('count')                    → "{{ count }}"
 *   rx('count').add(1)             → "{{ count + 1 }}"
 *   rx('user').dot('name')         → "{{ user.name }}"
 *   rx('items').length()           → "{{ items | length }}"
 *   rx('price').currency('USD')    → "{{ price | currency:'USD' }}"
 *   rx('active').then('Yes', 'No') → "{{ active ? 'Yes' : 'No' }}"
 */
export declare class Rx {
    private readonly expr;
    constructor(expression: string);
    /** Raw expression string without {{ }} wrapper */
    get expression(): string;
    /** Serialize to "{{ expression }}" template string */
    toString(): string;
    toJSON(): string;
    /** Dot-path access: rx('user').dot('name') → "{{ user.name }}" */
    dot(key: string): Rx;
    /** Index access: rx('items').at(0) → "{{ items.0 }}" */
    at(index: number | Rx): Rx;
    add(other: number | string | Rx): Rx;
    sub(other: number | string | Rx): Rx;
    mul(other: number | string | Rx): Rx;
    div(other: number | string | Rx): Rx;
    mod(other: number | string | Rx): Rx;
    eq(other: unknown): Rx;
    neq(other: unknown): Rx;
    gt(other: number | Rx): Rx;
    gte(other: number | Rx): Rx;
    lt(other: number | Rx): Rx;
    lte(other: number | Rx): Rx;
    and(other: Rx): Rx;
    or(other: Rx): Rx;
    not(): Rx;
    then(ifTrue: unknown, ifFalse: unknown): Rx;
    currency(code?: string): Rx;
    percent(decimals?: number): Rx;
    number(decimals?: number): Rx;
    round(decimals?: number): Rx;
    compact(decimals?: number): Rx;
    abs(): Rx;
    date(format?: string): Rx;
    time(): Rx;
    datetime(): Rx;
    upper(): Rx;
    lower(): Rx;
    truncate(maxLength: number): Rx;
    pluralize(word?: string): Rx;
    length(): Rx;
    join(separator?: string): Rx;
    first(): Rx;
    last(): Rx;
    selectattr(attr: string): Rx;
    rejectattr(attr: string): Rx;
    default(value: unknown): Rx;
    /**
     * Append an arbitrary pipe filter: `rx('x').pipe('humanName')` → `{{ x | humanName }}`
     *
     * Supports variadic args: `.pipe('date', 'long')` → `{{ x | date:'long' }}`
     * Use this for custom pipes registered via `registerPipe()`.
     */
    pipe(name: string, ...args: unknown[]): Rx;
}
/** Create an Rx expression referencing a state key */
export declare function rx(key: string): Rx;
/** Current item in a ForEach loop */
export declare const ITEM: Rx;
/** Current index in a ForEach loop */
export declare const INDEX: Rx;
/** Value from an interaction event (input value, checkbox state, etc.) */
export declare const EVENT: Rx;
/** Error message available in on_error callbacks */
export declare const ERROR: Rx;
/** Return value available in on_success callbacks */
export declare const RESULT: Rx;
/**
 * STATE proxy — convenience for accessing state keys.
 * Usage: STATE.foo → rx('foo'), STATE.user.name → rx('user.name')
 */
export declare const STATE: Record<string, Rx>;
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