You're seeing just the function
forage_select_filter, go back to ForageWeb.ForageView module for more information.
Link to this function
forage_select_filter(form, field, path, opts \\ )
%Phoenix.Html.Form.t/1)- the form
path(binary) - the URL from which to request the data
:foreign_key(optionsl) - The name of the foreign key (as a string or an atom). If this is not supplied it will default to