get allItems() {
      return this._getAllSubItems(this.items);
    }
Returns all slotted tabs and their subTabs in a flattened array.
The order of tabs is depth-first. For example, given the following slotted elements:
<pre><code>
	&lt;ui5-tabcontainer&gt;
		&lt;ui5-tab id="First" text="First"&gt;
			...
			&lt;ui5-tab slot="subTabs" id="Nested" text="Nested"&gt;...&lt;/ui5-tab&gt;
		&lt;/ui5-tab&gt;
		&lt;ui5-tab id="Second" text="Second"&gt;...&lt;/ui5-tab&gt;
		&lt;ui5-tab-separator id="sep"&gt;&lt;/ui5-tab-separator&gt;
		&lt;ui5-tab id="Third" text="Third"&gt;...&lt;/ui5-tab&gt;
	&lt;/ui5-tabcontainer&gt;
</code></pre>
Calling <code>allItems</code> on this TabContainer will return the instances in the following order:
<code>[ ui5-tab#First, ui5-tab#Nested, ui5-tab#Second, ui5-tab-separator#sep, ui5-tab#Third ]</code>
@public
@readonly
@name sap.ui.webc.main.TabContainer.prototype.allItems
@returns {sap.ui.webc.main.ITab[]}