[wix-users] Why does UIRef has to be under Directory Fragment?

[Shintaro Takechi]

Hi All,

I had the rare opportunity to start making a WiX installer from scratch
again.
It has been a while so I stumbled upon a couple things but following is the
biggest question I have.

I am making custom dialogs and am adding an UI with InstallUISequence in it
with the first dialog being <Show Before="ExecuteAction">.

Now I thought it was all good, but the UI did not show up.

Turns out that I did not place my UIRef underneath my directories fragment.
Instead, I had its own fragment.

Referring to this link (
https://wixtoolset.org/documentation/manual/v3/wixui/dialog_reference/wixui_installdir.html),
I see that UIRef is placed underneath the directory fragment.

Why is this? Why do I need to call UIRef underneath directories and nowhere
else?

This may be a very basic and fundamental question, but I had to ask.

Thank you.