/**
 * @summary Prepare a string for matching, per ITU Recommendation X.520, Section 7.
 * @description
 *
 * This function normalizes an input string for comparison in X.500 matching
 * rules according to the procedures defined in
 * [ITU Recommendation X.520 (2019)](https://www.itu.int/rec/T-REC-X.520/en),
 * Section 7.
 *
 * The input string is already expected to be transcoded, thereby satisfying
 * the procedures defined in section 7.1. There is nothing to be done relating
 * to section 7.5. There is work to be done only for `NumericString` types in
 * section 7.6.2, but those should simply be handled in the `NumericString`
 * matching rules; they will not be handled here.
 *
 * @param {string} str The string to be normalized.
 * @returns {string} The normalized string, or `undefined` if there was a prohibited character.
 *
 * @function
 */
export declare function prepString(str: string): string | undefined;
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