Need an example of using an asset with additional metdata.

According to [this Discord conversation](https://discord.com/channels/691052431525675048/1203681762719305758), the way to write an asset with additional metadata is to use an asset for the metadata file with a custom loader that will in turn load the underlying asset. But this pattern is not obviously correct, and there are no examples of it (that I could find). An example of how to do this sort of thing would be welcome.