onKeyPress_(event) {
        let method;
        let argument;

        if (DOM.isFocusableElement() || this.ws_.isDisabled()) {
            return;
        }

        switch (event.which) {
            case Keys.AV_PAGE:
                method = this.enable_ ? this.goNext : this.ws_.goNext;
                break;
            case Keys.SPACE:
                if (event.shiftKey) {
                    method = this.enable_ ? this.goPrev : this.ws_.goPrev;
                } else {
                    method = this.enable_ ? this.goNext : this.ws_.goNext;
                }
                break;
            case Keys.RE_PAGE:
                method = this.enable_ ? this.goPrev : this.ws_.goPrev;
                break;
            case Keys.HOME:
                method = this.ws_.goToSlide;
                argument = 0;
                break;
            case Keys.END:
                method = this.ws_.goToSlide;
                argument = this.ws_.maxSlide_ - 1;
                break;
            case Keys.DOWN:
                method = this.ws_.isVertical ? (this.enable_ ? this.goNext : this.ws_.goNext) : null;
                break;
            case Keys.UP:
                method = this.ws_.isVertical ? (this.enable_ ? this.goPrev : this.ws_.goPrev) : null;
                break;
            case Keys.RIGHT:
                method = !this.ws_.isVertical ? (this.enable_ ? this.goNext : this.ws_.goNext) : null;
                break;
            case Keys.LEFT:
                method = !this.ws_.isVertical ? (this.enable_ ? this.goPrev : this.ws_.goPrev) : null;
                break;

            case Keys.F:
                if (!event.metaKey && !event.ctrlKey) {
                    method = this.ws_.fullscreen;
                }

                break;
        }
        if (method) {
            method.call(this.enable_ ? this : this.ws_, argument);
            // Prevents Firefox key events.
            event.preventDefault();
        }
    }
Reacts to the keydown event. It reacts to the arrows and space key
depending on the layout of the page.
@param {KeyboardEvent} event The key event.
@private