Macro elements 

macro_rules! elements {
    () => { ... };
    ($($element:expr),+ $(,)?) => { ... };
}

Build a &[DataElement] from a mix of simple values and component lists.

Each entry is an arbitrary expression borrowed through AsDataElement: a string becomes a simple data element, an array or slice of strings becomes a composite. This is the shorthand for the mixed-segment shape that dominates real EDIFACT:

use edifact_rs::{Writer, elements};

// Runtime values, not just literals — the everyday builder shape.
let qualifier = String::from("MS");
let gln = "9900112233445";

let mut w = Writer::new(Vec::new());
w.write_elements("NAD", elements![qualifier.as_str(), [gln, "", "293"]])?;
w.write_elements("DTM", elements![["137", "20260101", "102"]])?;
assert_eq!(
    w.finish()?,
    b"NAD+MS+9900112233445::293'DTM+137:20260101:102'".to_vec(),
);

Composite components must be string slices: a [String; N] cannot borrow as &[&str] without allocating, so write [id.as_str(), "", agency].

The expansion borrows temporaries, so the result must be consumed within the same statement — passing it directly as an argument, as above, always is.