/**
* Validate a URL against an allowlist of safe protocols.
*
* Rejects `javascript:`, `vbscript:`, `file:`, non-image `data:`,
* and any other non-allowlisted scheme. Accepts absolute URLs and —
* when `base` is provided — relative URLs resolved against `base`.
*
* Returns the normalized href on success, or `null` if the URL is
* unparseable or uses a forbidden protocol.
*/
export declare function safeUrl(input: string, base?: string): string | null;
/**
* Escape characters that would change HTML semantics when rendered
* via `innerHTML`. Prefer `element.textContent = s` where possible;
* this helper exists for the handful of paths that must build a
* string (e.g. server-rendered markup, shadow DOM templates).
*/
export declare function escapeHtml(input: string): string;
/**
* Assert that a string does not carry a dangerous protocol even
* when used as a user-visible link target. Returns `true` when safe.
*/
export declare function isSafeUrl(input: string, base?: string): boolean;
/**
* Minimal shape of a Trusted Types policy object — just enough for
* the HTML caption sink. We intentionally do not depend on
* `@types/trusted-types`; the real browser objects are structurally
* compatible with this interface.
*/
export interface PencereTrustedTypePolicy {
	createHTML(input: string): string | TrustedHTML;
}
/**
* Create (and memoize) the `pencere` Trusted Types policy.
*
* Callers who opt into HTML captions are expected to supply a
* sanitizer — typically `DOMPurify.sanitize` — that returns a string.
* Under `require-trusted-types-for 'script'`, every `innerHTML`-like
* sink in pencere (currently only HTML captions) is routed through
* this policy so the sanitized output carries a `TrustedHTML` stamp.
*
* When Trusted Types is not exposed on the current window (Firefox,
* older Safari), returns a no-op shim that passes the string through
* unchanged — the caller's sanitizer is still the source of truth.
*
* Repeated calls with compatible options reuse the same policy object
* to avoid the "Policy pencere already exists" CSP violation.
*
* @example
* ```ts
* import DOMPurify from "dompurify"
* import { createTrustedTypesPolicy } from "pencere"
*
* const policy = createTrustedTypesPolicy({
*   sanitize: (html) => DOMPurify.sanitize(html),
* })
* element.innerHTML = policy.createHTML(userHtml) as string
* ```
*/
export declare function createTrustedTypesPolicy(options?: {
	/** User-supplied HTML sanitizer. Defaults to identity (unsafe!). */
	sanitize?: (html: string) => string;
	/** Policy name. Defaults to `"pencere"` to match the CSP cookbook. */
	name?: string;
}): PencereTrustedTypePolicy;
/** Visible for tests — reset the memoized policy between cases. */
export declare function _resetTrustedTypesPolicy(): void;