When you need to implement a parser for a structure, you could add the following code:

defmodule MyStruct do
  use Proximal.Document
  alias Proximal.Xmlel

  defstruct [:name, :surname]

  @impl Proximal.Document
  def render(%__MODULE__{name: name, surname: surname}) do
    Xmlel.new("mystruct", %{}, [
      Xmlel.new("name", %{}, [name]),
      Xmlel.new("surname", %{}, [surname])
    ])
  end
end

The code should let you to create your data in the way you need and thanks to the implementation of the render/1 function, you could use:

%MyStruct{name: "Manuel", surname: "Rubio"}
|> Proximal.to_xmlel()

To get the representation in %Xmlel{} structs and even adding at the end of that pipe to_string/1 to get the XML in a string.