#[macro_rules_attribute]Expand description
Legacy name for what is currently named #[apply]
Despite being a slightly clearer name (than #[apply] is) w.r.t. what it
does, #[macro_rules_attribute] had the big drawback of being a mouthful.
Hence the #[apply] alias being born, and now even superseding
#[macro_rules_attribute] altogether as the author-deemed “idiomatic”
name to favor.