/**
 * Returns the specified value as a boolean.\
 * This function will only consider values of type boolean and the strings "true" or
 * "false" (case insensitive) as boolean values.
 * @param value The value to be converted.
 * @param defaultValue The value to be returned if value cannot be converted to a boolean.
 * @returns value as a boolean or defaultValue if value cannot be converted to a boolean.
 * @throws [[ConversionError]] If value cannot be converted to a boolean and defaultValue
 *                             is not provided.
 */
export declare function toBoolean(value: unknown, defaultValue?: boolean): boolean;