How to save inserted tag in CKEDITOR5?

Question

CKEditor

I'm trying to do it according to the manual.

import Plugin from '@ckeditor/ckeditor5-core/src/plugin';
import Widget from '@ckeditor/ckeditor5-widget/src/widget';
import InsertTooltipCommand from './inserttooltipcommand';
import { toWidget } from '@ckeditor/ckeditor5-widget/src/utils';

export default class TooltipEditing extends Plugin {
    static get requires() {
        return [ Widget ];
    }

    init() {
        this._defineSchema();
        this._defineConverters();

        this.editor.commands.add('insertTooltip', new InsertTooltipCommand(this.editor));
    }
    
    

    _defineSchema() {
        const schema = this.editor.model.schema;

        schema.register('tooltip', {
            // Behaves like a self-contained object (e.g. an image).
            isObject: true,
            isInline: true,
            allowIn: 'paragraph',
            allowAttributes: [ 'class', 'content' ]
        });
    }

    _defineConverters() {
        const conversion = this.editor.conversion;
        
        
        conversion.for('editingDowncast').elementToElement({
            model: 'tooltip',
            view: (modelElement, downcastWriter) => {
                const title = prompt( 'Текст' );
                const header = prompt( 'Заголовок' );
                const content = prompt( 'Содержание' );
                
                const div = downcastWriter.createContainerElement('span', { class: 'p-post__tooltip', content: '<button class="b-button _plain" type="button" > <span class="b-icon _close"></span> </button> <h3>'+header+'</h3><p>'+content+'</p>' });
                const text = downcastWriter.createText(title);
                downcastWriter.insert(downcastWriter.createPositionAt(div, 0), text);
                return toWidget(div, downcastWriter, { label: 'tooltip widget' });
            }
        });
    }
}

https://pix.my/FoyQ3J is inserted into the content body itself, but after saving there is nothing.