pub fn type_doc(name: &str) -> Option<&'static str>Expand description
The description of the built-in type name denotes, or None for any
other name.
Type position is a different question from value position and gets a
different answer: Int is a type and never a value, Range is a type whose
name no value shares, and the nine collection names are both — so this looks
in BUILTIN_TYPES first and falls back to PRELUDE, where Vec’s row
already opens with what a Vec is before it says what Vec() builds.
The fallback is what keeps Vec[Int] from needing a second description of a
Vec that could drift from the first.