When setting the priors for a model which does include splines, we can specify the prior of class “sds” for the wiggliness parameter, which is in some literature referred as a hyperprior.
But how could we specify the prior for the parameters of the actual spline, i.e. the prior for the “linear” coefficients in the mixed model representation (which are denoted as beta in Wood (2017), but other authors mostly use alpha or gamma)?
Besides feeling uncomfortable when using the default prior without knowing it, the bigger issue is that for specific problems the authors suggest different priors (e.g. RW1, RW2, i.i.d., …).