/**
 * CSS token scanning for the D53 unsafe-CSS gates.
 *
 * Both gates ask a question about CSS *tokens*: "does this stylesheet declare
 * an `@import` at-rule" and "does a `url()` name a relative address". Text
 * scanning answers neither, and it fails in both directions at once: a `)`
 * inside a quoted URL ends a regex match early, so `url("./mark).svg")` — a
 * legal reference to a legal filename — matches nothing and walks past the
 * gate into a production build that 404s; while a `url(...)` written inside a
 * string literal, which is text and not a reference at all, matches and gets
 * refused. One scanner, reading the token grammar, is what both gates need,
 * so both read the stream produced here instead of writing a private regex.
 *
 * Coverage is CSS Syntax Level 3 tokenization as far as those two questions
 * reach: comments, strings (escapes, line continuations, bad-string), ident
 * sequences, at-keywords, function tokens, and both url forms (the unquoted
 * url-token and the `url(` function over a string), including bad-url
 * recovery. Selectors, declarations, at-rule blocks, and numeric detail stay
 * unparsed — CSS remains raw and unowned under D53, and this is a reader of
 * addresses, not a CSS parser.
 */
/** A token one of the unsafe-CSS gates asks about. */
export type CssToken = 
/** `@import`, `@media`, … — the at-rule name, escapes already decoded. */
{
    readonly kind: "at-keyword";
    readonly name: string;
}
/** A `url()` address, escapes decoded, exactly what a browser resolves. */
 | {
    readonly kind: "url";
    readonly value: string;
}
/** A bare string that the image-set grammar defines as a URL. */
 | {
    readonly kind: "asset-address";
    readonly value: string;
    readonly syntax: "image-set" | "-webkit-image-set";
};
/**
 * Yields the at-keyword and url tokens of a stylesheet. Every other token is
 * still tokenized — that is the whole point, a string is skipped as a string
 * and a comment as a comment — it is simply not reported.
 */
export declare function cssTokens(source: string): Generator<CssToken>;
/**
 * True when `value` is one balanced CSS declaration value: text a generated
 * rule can place after `property:` with no way to end that declaration, the
 * rule around it, or the stylesheet segment the rule lives in.
 *
 * A Look property's value reaches the DOM through `setProperty` on a custom
 * property and cannot escape, which is why the value vocabulary deliberately
 * accepts arbitrary text for the `text`, `filter`, `transform`, and
 * `animation` kinds (D73 rule 187). `keyframes:` reuses that same checker on a
 * path that concatenates into stylesheet text instead, so a `}` in a stop's
 * value closed the generated rule and everything after it became author-owned
 * CSS in the compiler-owned segment. This is the gate for the concatenating
 * path only: `{`, `}`, `;`, and `@` never appear outside a string, parens
 * balance, and strings and comments terminate.
 */
export declare function isCssDeclarationValue(value: string): boolean;
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