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A general description is here.
In ‘*.Rd’ help files, the \linkS4class macro now also works for links to other packages via \linkS4class[<pkg>]{<myClass>}, much nicer than the “workaround” \link[<pkg>:<myClass>-class]{<myClass>} necessary in earlier versions of R.
Packages with the new syntax need to formally depend on ‘R >= 4.6.0’.