/**
 * Hyperoptimized camelCase conversion.
 *
 * Single-pass, zero-regex, zero-allocation (beyond the result string).
 * Splits on non-alphanumeric separators and case transitions:
 *   - lowercase/digit followed by uppercase  (e.g. fooBar  → foo|Bar)
 *   - uppercase followed by uppercase+lower   (e.g. HTMLParser → HTML|Parser)
 *
 * First word is lowercased; subsequent words are capitalized (first char
 * uppercased, rest lowercased). A subsequent word that starts with a digit
 * is prefixed with '_'.
 */
export declare function camelCase(input: string): string;