/**
 * Content sniffing for text-shaped image formats.
 *
 * SVG is markup, so it has no byte signature — but it does have an unambiguous
 * root element, and identifying it matters twice over: the detector routes SVG
 * to the sanitizer rather than to a vision API, and the image path must not let
 * SVG bytes travel under some other format's MIME type.
 *
 * ## Why this is a scan and not a regular expression
 *
 * The obvious implementation strips the prolog with a pattern like
 * `(?:<!--[\s\S]*?-->\s*)*<svg`. That is two nested quantifiers, and CodeQL
 * rightly flags it as `js/redos`: input beginning `<!--` and repeating
 * `--><!--` drives exponential backtracking, so a hostile (or merely odd)
 * upload can burn CPU inside what is supposed to be a cheap type check.
 *
 * The `.replace()`-chain alternative is unsound for a different reason —
 * removing a multi-character construct can join the surrounding text into a
 * fresh instance of that same construct, so one pass does not converge
 * (`<!--<!-- -->-->` leaves a comment behind). CodeQL flags that shape too, as
 * `js/incomplete-multi-character-sanitization`.
 *
 * A single forward scan has neither problem: the cursor only ever advances, so
 * the work is linear in the input and no construct can re-form behind it.
 *
 * @module utils/markupSniff
 */
/**
 * Whether the leading bytes are an SVG document.
 *
 * Requires `<svg` to be the *root element* rather than merely present, so an
 * HTML page embedding an inline `<svg>` icon is not mistaken for a standalone
 * image. A BOM, XML declaration, DOCTYPE and comments may precede it.
 *
 * @param input - Buffer or string to inspect; only the head is read.
 */
export declare function looksLikeSvgMarkup(input: Buffer | string): boolean;