Great idea, thank you!
I nested another Wayfinder call in the &innerTpl:
<div class="dropdown_container">
[[Wayfinder?
&startId=`2`
&outerClass=`dropdown_flyout`
&innerClass=`dropdown_flyout_level`
&parentClass=`dropdown_parent`
]]
</div>
As I set the id on 2, EVERY sub menu starts on this Main Page (SERVICES). But I have other main pages i.e. ABOUT with a sub menus on its on. So I tried &startId=`[[*parent]]` because I need the id of the particular parent main page. And what happens? I get a list of all my main pages in the sub menu (Home, Services, About, ...). But I need a list of the pages WITHIN the particular main page container. Is there a way to get a relative parent id within the &startid parameter?
This is the site structure:
<ul class="menu">
<li>HOME</li>
<li>SERVICES (main page with the first sub menu, has id=2)
<div class="dropdown_container">
<ul class="dropdown_flyout">
...
<ul class="dropdown_flyout_level">
...
<ul class="dropdown_flyout_level">
</div> ...
</li>
<li>ABOUT (main page with another sub menu)
<div class="dropdown_container">
<ul class="dropdown_flyout">
[the start id of this sub menu should be the one of the ABOUT container]
</ul>
</div>
</li>
...
</ul>