Custom constrained expression

The Stan language offers built-in support for bounded parameters like real<lower=1,upper=2> pt. How do I put an expression inside a constrained region? For example,

transformed data {
  real lb = 1;
  real ub = 2;
parameters {
  real part1;
  real part2;
transformed parameters {
  real pt = part1 + part2;
  real bounded = logit((pt - lb)/(ub - lb));
model {
  part1 ~ std_normal();
  part2 ~ std_normal();

This is similar to the built-in scaled and translated log-odds transform. Can I just do this and add the absolute Jacobian of pt?

I’m aware that the simple example I wrote here isn’t identified. I plan to build up a multilevel regression so part1 and part2 would have different grouping structures.


Nevermind. Maybe I don’t need this for my model specification.