Macro dot_generator::node_id

macro_rules! node_id {
    () => { ... };
    ($e : expr) => { ... };
    ($e : expr, $p : expr) => { ... };
    ($i : ident $e : expr) => { ... };
    ($i : ident $e : expr, $p : expr) => { ... };
}

represents a node id in dot lang Essentially it is a combination of id and port