Constant VALID_FRAGMENT_NAMES_MSG

pub(crate) const VALID_FRAGMENT_NAMES_MSG: &str = "valid fragment specifiers are \
    `ident`, `block`, `stmt`, `expr`, `pat`, `ty`, `lifetime`, `literal`, `path`, \
    `meta`, `tt`, `item` and `vis`, along with `expr_2021` and `pat_param` for edition compatibility";