As posteriors are priors that have been updated after observing some data, the goal of this function is to un-update the posteriors to obtain models representing the priors. These models can then be used to examine the prior predictive distribution, or to compare priors with posteriors.

## Usage

```
unupdate(model, verbose = TRUE, ...)
# S3 method for stanreg
unupdate(model, verbose = TRUE, ...)
# S3 method for brmsfit
unupdate(model, verbose = TRUE, ...)
# S3 method for brmsfit_multiple
unupdate(model, verbose = TRUE, newdata = NULL, ...)
# S3 method for blavaan
unupdate(model, verbose = TRUE, ...)
```