import { Plugin } from 'unified';
import { DastRoot } from '../packages/parser/dist';
/**
 * Upgrade references with attribute syntax.
 * ```xml
 *   $x{foo="bar"}
 * ```
 * becomes
 * ```xml
 *   <copy source="x" foo="bar" />
 * ```
 * This must happen **before** the `upgradeCopySyntax` plugin resolves all the copy
 * elements.
 */
export declare const upgradeAttributeSyntax: Plugin<[], DastRoot, DastRoot>;
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