/**
 * A copy of the tnt.tree.node_display.circle function. This version has a
 * callback function as an optional parameter. The D3 selection is given to the
 * callback function, allowing application-specific modifications to be made to
 * the selection.
 *
 * @param callback The callback function that will be applied to the D3 selection.
 *
 * @returns The original tnt.tree.node_display.circle with the callback applied
 * to the D3 selection.
 */
export declare const circle: (callback?: any) => any;
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