import { MessageFunctionType, Result } from '../types';
export interface IsSubStringErrors {
    TARGET_ARGUMENT_NOT_A_STRING: MessageFunctionType;
    CONTAINED_ARGUMENT_NOT_A_STRING: MessageFunctionType;
}
export declare const IS_SUBSTRING_ERRORS: IsSubStringErrors;
/**
 * Checks if the value is a substring of the target.
 * ### Example
 * ```
 * expect(isSubString('foo', 'fooboo').value).toBeTruthy()
 * ```
 * @param contained The value that may be contained.
 * @param target The target value to perform the check against.
 */
export declare function isSubString(contained: string, target: string): Result<boolean | undefined>;