you can just have an unnamed slot. I'm probably missing something here haven't build a tabs thing in a long time. But just trying this out for a couple of minutes the thing you want seems to be possible. I didn't do any styling here and the code is just something I hacked down to test it. Where hn-tabs is your tab-area and hn-tab your tab-

   class HnTabs extends HTMLElement {
       constructor() {
           super();
           this._tabs = {}
           this.attachShadow({ mode: 'open' })
           const ul = document.createElement('ul')
           this.shadowRoot.appendChild(ul)
           const slot = document.createElement('slot')         
           this.shadowRoot.appendChild(slot)
           slot.addEventListener('slotchange', () => {
             ul.innerHTML = ''
             const tabs = Array.from(this.querySelectorAll('hn-
             if (!tabs.some((tab) => tab.hasAttribute('active')
               tabs[0].setAttribute('active', '')
             }
             tabs.forEach((tab) => {
               const li = document.createElement('li')
               li.innerText = tab.getAttribute('text')
               ul.appendChild(li)
               li.addEventListener('click', (e) => {
                 tabs.forEach((t) => t.removeAttribute('active'
                 tab.setAttribute('active', '')
               })
             })
           })
       }
   }
   customElements.define('hn-tabs', HnTabs);
   
   class HnTab extends HTMLElement {
       static get observedAttributes() {
         return ['active'];
       }
       constructor() {
           super()
           this.attachShadow({ mode: 'open' });
           this._slot = document.createElement('slot')         
           this.shadowRoot.appendChild(this._slot)
           this._slot.style.display = 'none'
           console.log(this.slot)
       }
       attributeChangedCallback() {
         this.#activeStatus()
       }
       connectedCallback() {
         this.#activeStatus()
       }
       #activeStatus(){
         const active = this.hasAttribute('active');
         this._slot.style.display = active ? 'block' : 'none'
       }
   }
   customElements.define('hn-tab', HnTab);