/**
 * Every asset URL the subtree references, absolute, sorted, de-duplicated.
 *
 * Sorted because the result is folded into a digest through an object key order
 * nobody should have to reason about, and a list whose order depends on document
 * traversal is a list that will one day differ for a reason nobody can name.
 *
 * Schemes that carry their own bytes — `data:` — are excluded: the bytes are
 * already in the document, so hashing them again would put the same information
 * in the key twice and make an inline SVG look like a fetch. `blob:` and
 * `about:` are excluded because nothing on the wire corresponds to them.
 */
export declare function referencedAssets(root: Element): readonly string[];
/** An attribute that names a file: `srcset` names one per candidate. */
export interface FileAttribute {
    readonly name: string;
    readonly namespace: string | null;
    readonly candidates: boolean;
}
/**
 * The attributes that name a file, by element.
 *
 * `href` is read only on SVG's `<use>` and `<image>`. On an `<a>` it is a
 * destination rather than an asset, and hashing every link target would put the
 * whole site in one subject's key.
 *
 * **Every `srcset` candidate, not the one the browser picked.** Which candidate
 * is used depends on the device pixel ratio, and a key that recorded only the
 * chosen one would let a 2× asset change without moving the 1× runner's key —
 * the same file, the same URL list, and a baseline that is quietly of different
 * bytes. Over-inclusion here costs a re-render nobody needed; under-inclusion
 * costs a false `unchanged`.
 */
export declare function fileAttributes(element: Element): readonly FileAttribute[];
/** One candidate in a `srcset`: its URL, and the descriptor offered with it. */
export interface SrcsetCandidate {
    readonly url: string;
    /** `2x`, `640w`, or empty. */
    readonly descriptor: string;
}
/**
 * `a.png 1x, b.png 2x` → each URL with its descriptor, by HTML's rule.
 *
 * A URL is a run of anything but ASCII whitespace, so the comma inside a `data:` URL is part of
 * it: splitting on every comma cut such a URL in two, and the second half
 * resolved as a file next to the page. A comma ends a candidate only after its
 * URL, or trailing it.
 */
export declare function srcsetCandidates(value: string): readonly SrcsetCandidate[];
/**
 * The observed assets, narrowed to the ones this subject references.
 *
 * Where the two halves meet: the driver knows the bytes and the page knows the
 * subject. Returned as a plain object because that is what `EnvironmentInputs`
 * carries, and built in referenced order so the shape is stable.
 *
 * An asset the page's own origin serves is keyed by its path. A collector serves
 * a build on whatever port the machine had free, and a key holding that port
 * makes one build served twice two environments. An asset from another origin
 * keeps its absolute URL, because there the host is part of what was fetched.
 */
export declare function assetsFor(root: Element, observed: Readonly<Record<string, string>>): Readonly<Record<string, string>>;
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