Question Dynamic defaultValue in UxmlAttributeDescription

I have a custom component which I want to add a persistent guid to.
That guid is generated anew for each new element. Yet, I am lacking a way to actually persist it into the xml.

The code blow populates the field with a new guid. Yet it does so every time a new instance is created and it is not saved in the xml.

Code (csharp):

1. public new class UxmlTraits : VisualElement.UxmlTraits
2. {
3.    UxmlStringAttributeDescription _guid = new UxmlStringAttributeDescription { name = "Guid", defaultValue = System.Guid.NewGuid().ToString() };
4. }

This seems logical to me. The default value should always be the same and therefore the UI Builder treats it as if it were.

Now here is what I want. After the first initialization I want the guid to have a value set which is not the default and which is stored in the xml if the save button is pressed. It would look like this:



I do have a proof-of-concept solution which involves a lot of reflection. Basically I am filling the m_Properties list of the UXMLAsset after initialization. I am not even 100% sure this works in all cases. It's very nasty.

Here comes my question:

Is there a public API to SET the value of UXML properties?
Like the inverse of what

GetValueFromBag(bag, cc);

does.

Thank you.