My main toolbar has a sub-toolbar to group and style particular toolbar elements roughly laid out follows:
<div id="editor-container">
<div id="toolbar">
<span class="ql-formats">
<button class="ql-bold"></button>
<button class="ql-italic"></button>
</span>
<div id="sub-toolbar">
<span class="ql-formats">
<button id="sub-button">sub-button</button>
</span>
</div>
</div>
<div id="editor"></div>
</div>
It isn't clear how to add a dynamic drop box to the sub-toolbar in my example. It just adds after the #sub-toolbar div on calling myDropDown.attach(quill) as per your drop down box example.