PrimalSearch environment. How do I retrieve fixed variables' values?

[lkmaks]

In these docs https://doc.ecole.ai/py/en/stable/reference/environments.html#primalsearch,
it says that to make an action we have to provide a partial assignment of variables from action_set .
Size of action_set can be smaller than obs.column_fatures.shape[0], and the latter seems to always be same as the number of variables in the initial problem. Where from observation or elsewhere can I acquire what the other variables are fixed to? Are they guaranteed to be fixed to 0 or 1, and are all discrete variables binary in ecole? Where and which docs is it reflected?

Would be grateful for any help.