[accordion] Allow multiple panels to be opened at the same time

[chanar]

Currently only one panel can be opened at the same time. should have attribute to control this functionality. opened-close="true/false"

https://github.com/vaadin/vaadin-accordion/blob/master/src/vaadin-accordion.html#L232

[chanar]

Meanwhile extended AccordionElement to allow multiple panels to be opened

class ModifiedVaadinAccordion extends AccordionElement {
  _updateOpened(e) {
    const target = this._filterItems(e.composedPath())[0];
    const idx = this.items.indexOf(target);

    if (e.detail.value) {
      if (target.disabled || idx === -1) {
        return;
      }

      this.opened = idx;

    } else if (!this.items.some(item => item.opened)) {
      this.opened = null;
    }
  }

  _updateItems(items, opened) {
    if (items) {
      const itemToOpen = items[opened];
      if (itemToOpen) {
        itemToOpen.opened = true
      }
    }
  }
}

[AirbornePanda]

Hi, are there any plans on adding this feature in the future?

[Misiu]

I also need that.
@web-padawan can this get added in 2.0.0?