Manual talk:Page content models/Flow

Where should be the placed the code to write the goat name in dababase in the provided example. Is it with Manual:Hooks/EditPage::attemptSave:after but I have to use $_POST and I do not how how to code preview that should not update database.

Can you clarify a bit more what is needed? First of all, I think you can convert an already-existing page to your "goat" content model. This can be done from the "info" page. That answers your need, since it's then written in the database, so it triggers your custom "goat renderer".