Macro template 

macro_rules! template {
    (Word) => { ... };
    (Word, $link: literal) => { ... };
    (List: $descr: expr) => { ... };
    (List: $descr: expr, $link: literal) => { ... };
    (OneOf: $one_of: expr) => { ... };
    (NameValueStr: [$($descr: literal),* $(,)?]) => { ... };
    (NameValueStr: [$($descr: literal),* $(,)?], $link: literal) => { ... };
    (NameValueStr: $descr: literal) => { ... };
    (NameValueStr: $descr: literal, $link: literal) => { ... };
    (Word, List: $descr: expr) => { ... };
    (Word, List: $descr: expr, $link: literal) => { ... };
    (Word, NameValueStr: $descr: expr) => { ... };
    (Word, NameValueStr: $descr: expr, $link: literal) => { ... };
    (List: $descr1: expr, NameValueStr: $descr2: expr) => { ... };
    (List: $descr1: expr, NameValueStr: $descr2: expr, $link: literal) => { ... };
    (Word, List: $descr1: expr, NameValueStr: $descr2: expr) => { ... };
    (Word, List: $descr1: expr, NameValueStr: $descr2: expr, $link: literal) => { ... };
    (@ $word: expr, $list: expr, $one_of: expr, $name_value_str: expr, $link: expr) => { ... };
}

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