Hi!
In fact, event if fragments are not presented as a selection option in the dropdown list of available views, they are still available as a nested element in the view.
To explain it more clearly, I will show you an example.
Let’t imagine that I have a fragment like this in my project:
<fragment xmlns="http://jmix.io/schema/flowui/fragment">
<content>
<vbox id="root">
<button id="button" text="Button"/>
<hbox id="layout">
<span id="span" text="Span"/>
</hbox>
</vbox>
</content>
</fragment>
And I added this fragment to my BlankView:
<view xmlns="http://jmix.io/schema/flowui/view"
title="msg://blankView.title">
<layout>
<fragment id="fragment" class="com.company.bugfix251.view.blankfragment.BlankFragment"/>
</layout>
</view>
When trying to set UI constraints policies for the BlankView, nested components from the fragment will be available for selection:

As for selection components ID from MainView, it also works as far as I can see:

This way you can use UI Constraints policy with both fragments and the MainView.
As for your second question, about inline search in view and component dropdown. That works too, as far as I can see:


Best regards,
Dmitriy