Accessibility: collapses buttons do not have aria-expanded information as default

[saskiaw]

Describe the problem to be solved
For accessibility reason a button, hoe is a collapse button, needs to have information about it before clicking on in.

Describe the solution you'd like
A collapse button like > 200 OK. has more infomation to show after clicking on it:

But in de code there is no information to find for it:

After clicking on it then it contains the infomation of it:

Describe alternatives you've considered
My question is if it is possible for collapse button to add information: aria-expanded="false". Then a page reader software has the chance to indicate that there is more to find.