/**
 * High-performance string format validation utilities.
 * These functions are optimized for maximum performance.
 */
/**
 * Validates if a string contains only ASCII characters (0-127).
 * This is highly optimized for performance.
 */
export declare const isAscii: (str: string) => boolean;
/**
 * Validates if a string represents valid UTF-8 when encoded.
 * JavaScript strings are UTF-16, but we need to validate they don't contain
 * invalid Unicode sequences that would produce invalid UTF-8.
 *
 * This checks for:
 * - Unpaired surrogates (invalid UTF-16 sequences)
 * - Characters that would produce invalid UTF-8
 */
export declare const isUtf8: (str: string) => boolean;
/**
 * Validates a string according to the specified format.
 */
export declare const validateStringFormat: (str: string, format: "ascii" | "utf8") => boolean;
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