Constant rustc_expand::mbe::quoted::VALID_FRAGMENT_NAMES_MSG_2021

source ยท 
pub(crate) const VALID_FRAGMENT_NAMES_MSG_2021: &str = "valid fragment specifiers are \
    `ident`, `block`, `stmt`, `expr`, `expr_2021`, `pat`, `ty`, `lifetime`, `literal`, `path`, \
    `meta`, `tt`, `item` and `vis`";