Macro rustc_feature::builtin_attrs::template

macro_rules! template {
    (Word) => { ... };
    (List : $descr : expr) => { ... };
    (NameValueStr : $descr : expr) => { ... };
    (Word, List : $descr : expr) => { ... };
    (Word, NameValueStr : $descr : expr) => { ... };
    (List : $descr1 : expr, NameValueStr : $descr2 : expr) => { ... };
    (Word, List : $descr1 : expr, NameValueStr : $descr2 : expr) => { ... };
    (@ $word : expr, $list : expr, $name_value_str : expr) => { ... };
}

A convenience macro for constructing attribute templates. E.g., template!(Word, List: "description") means that the attribute supports forms #[attr] and #[attr(description)].