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)].