/**
 * Prepends `0` before a bare leading decimal separator so `.5` → `0.5` (and `-.5` → `-0.5`).
 * Intended to run inside the sanitization pipeline AFTER `removeLeadingZeros`, since stripping
 * `0.5` → `.5` is exactly the case this reverses.
 */
export declare function prependLeadingZero(value: string, decimalSeparator?: string): string;