import { ElementRef } from '@angular/core';
import { MdcCharacterCounter } from './character-counter';
export declare class MdcHelperText {
    elementRef: ElementRef<HTMLElement>;
    characterCounter: boolean;
    id?: string;
    get persistent(): boolean;
    set persistent(value: boolean);
    private _persistent;
    get validation(): boolean;
    set validation(value: boolean);
    private _validation;
    _helperTextElement?: ElementRef<HTMLElement>;
    _characterCounterElement?: MdcCharacterCounter;
    constructor(elementRef: ElementRef<HTMLElement>);
    private _foundation;
    get foundation(): any;
    /** Sets the validity of the helper text based on inputIsValid. */
    setValidity(inputIsValid: boolean): void;
    /** Makes the helper text visible to the screen reader. */
    showToScreenReader(): void;
    init(foundation: any): void;
    addHelperTextClass(className: string): void;
    private _createAdapter;
}