/**
 * Converts a string to camelCase.
 *
 * Extracts word-like tokens (letter runs, digit runs, emoji) from the input,
 * lowercases the first token, and title-cases the rest. Acronyms like `HTML`
 * are folded to a single capitalized word (`Html`); non-letter/digit separators
 * (spaces, hyphens, underscores, punctuation) are dropped; emoji are preserved.
 *
 * Returns an empty string when the input contains no extractable tokens.
 *
 * @example
 * stringToCamelCase('FooBar')          // 'fooBar'
 * stringToCamelCase('foo-bar')         // 'fooBar'
 * stringToCamelCase('FOO_BAR')         // 'fooBar'
 * stringToCamelCase('XMLHttpRequest')  // 'xmlHttpRequest'
 * stringToCamelCase('xhr2 request')    // 'xhr2Request'
 */
export declare function stringToCamelCase(str: string): string;