 after the user's cursor and a popup element, 
use `aria-autocomplete="both"` 

Combobox with autocomplete list example:

```
<label for="comboInput">State</label>
<div class="combobox">
    <div class="cbPrimary">
    <input type="text" id="comboInput" class="cbEdit"
        role="combobox" aria-autocomplete="list"
        aria-haspopup="listbox" aria-expanded="true"
        aria-controls="popup_listbox" aria-activedescendant="cb-ak" />
    <button id="cbButton" tabindex="-1" aria-label="Open">▼</button>