import { AbstractValidator } from '../types';
/** Constraints to validate a `boolean` with. */
export interface BooleanConstraints {
    /**
     * Allow booleans to be parsed from strings (default: `false`).
     *
     * The string in question _MUST_ be either `true` or `false`, and will be
     * compared regardless of case.
     */
    fromString?: boolean;
}
/** A `Validator` validating `boolean`s. */
export declare class BooleanValidator extends AbstractValidator<boolean> {
    readonly fromString: boolean;
    constructor(constraints?: BooleanConstraints);
    validate(value: unknown): boolean;
}
export declare function booleanValidatorFactory(constraints: BooleanConstraints): BooleanValidator;
/** The `Validator` for `boolean`s. */
export declare const boolean: typeof booleanValidatorFactory & BooleanValidator;