New style is allow(foo), warn(foo), deny(foo) and forbid(foo), mirrored by -A foo, -W foo, -D foo and -F foo on command line. These replace -W no-foo, -W foo, -W err-foo, respectively. Forbid is new, and means "deny, and you can't override it".
//! kind
//~ kind
conflict with the new single-line-sugared-inner-doc-comment (`//! ...`).