/**
 * Dependency-free contract for unused-rule and critical-CSS engines.
 *
 * Core owns validation and resource limits. Extensions own parser/vendor
 * imports and their implementation-specific configuration.
 *
 * @module extensions/css/css-purging-engine
 */
export declare const CSSPurgingEngineName: "CSSPurgingEngine";
export declare const MAX_CSS_PURGING_ENGINE_IDENTITY_CHARACTERS = 256;
export interface CSSPurgeContentSource {
    readonly raw: string;
    readonly extension: string;
}
export interface CSSPurgingRequest {
    readonly css: string;
    readonly content: readonly CSSPurgeContentSource[];
    readonly safelist: readonly string[];
    readonly includeRejectedCSS: boolean;
}
export interface CSSPurgingResult {
    readonly css: string;
    readonly rejectedCSS?: string;
}
export interface CSSPurgingEngine {
    /**
     * Includes every implementation/version input capable of changing output.
     * Represented state must remain immutable for the captured engine lifetime.
     */
    readonly cacheIdentity: string;
    purge(request: CSSPurgingRequest): Promise<CSSPurgingResult>;
}
export declare function assertCSSPurgingEngine(value: unknown): asserts value is CSSPurgingEngine;
/** Capture identity and method once so registry mutation cannot split a run. */
export declare function captureCSSPurgingEngine(value: unknown): CSSPurgingEngine;
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