Non-zero prior mean for fixed-effects

[randel]

Hello! For fixef.prior , it is in the format normal(sd = c(10, 2.5), cov, common.scale = TRUE) and it says Normal priors are constrained to have a mean of 0 - non-zero priors are equivalent to shifting covariates. Could you explain why non-zero priors are equivalent to shifting covariates?

Or how hard is it to allow non-zero fixed-effects priors? Do you have any clue how to incorporate the prior mean for fixed-effects? Thanks!