Demo.Accounts.User.input

You're seeing just the function input, go back to Demo.Accounts.User module for more information.

Validates that the keys in the provided input are valid for at least one action on the resource.

Raises a KeyError error at compile time if not. This exists because generally a struct should only ever be created by Ash as a result of a successful action. You should not be creating records manually in code, e.g %MyResource{value: 1, value: 2}. Generally that is fine, but often with embedded resources it is nice to be able to validate the keys that are being provided, e.g

Resource
|> Ash.Changeset.for_create(:create, %{embedded: EmbeddedResource.input(foo: 1, bar: 2)})
|> MyApp.Api.create()