Quoting

quote_m2! constructs an M2 TokenStream from Rust tokens. $(...) interpolates any Rust expression implementing Lex. Each interpolation is first emitted as a real fragment, so punctuation, identifiers, literals, and groups compose according to their actual token boundaries rather than the Rust expression’s type. Parentheses, brackets, braces, and M2 angle bars are emitted as recursive raw groups.

$[pattern in iterator] { ... } repeats a recursively quoted template using an ordinary Rust for loop. The iterator and pattern are explicit; interpolations that do not depend on the pattern are reused normally on each iteration.

#![allow(unused)]
fn main() {
use m2_syn::{Span, Symbol, quote_m2};

let value = Symbol::new("value", Span::detached());
let tokens = quote_m2! {
    result = $(value) + 1;
    return result
};

assert_eq!(tokens.to_string(), "result=value+1;return result");

let values = [
    Symbol::new("left", Span::detached()),
    Symbol::new("right", Span::detached()),
];
let comma = m2_syn::Token![,](Span::detached());
let repeated = quote_m2! {
    $[value in &values] { $(value) $(comma) }
};
assert_eq!(repeated.to_string(), "left,right,");
}

The rendered text is normalized M2 source, not a lossless reproduction of whitespace or comments discarded by the typed graph.