Ash.Changeset.ensure_selected
You're seeing just the function
ensure_selected, go back to Ash.Changeset module for more information.
Ensures that the given attributes are selected.
The first call to select/2 will limit the fields to only the provided fields.
Use ensure_selected/2 to say "select this field (or these fields) without deselecting anything else".
See select/2 for more.