Rust Trick for Repetitive Documentation

via Valentine Briese :transuwu:: Little bit of a trick I discovered for documenting fields which are on multiple structures:

macro_rules! extensions_doc {
    () => {
        r#"The extensions properties are implemented as patterned fields that are always prefixed by `"x-"`."#
    };
}

pub struct Info {
    // ...
    #[doc = extensions_doc!()]
    pub extensions: HashMap<String, Value>,
}