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A general description is here.
‘is.R()’ is deprecated as no other S dialect is known to be in use (and this could only identify historical dialects, not future ones).
Further information on calls can be obtained by setting the environment variable ‘_R_DEPRECATED_IS_R_’ to ‘error’ which turns the deperecation warning into an error and so by default gives a traceback. (This is done by ‘R CMD check --as-cran’.)
‘UseMethod()’ no longer forwards local variables assigned in the generic function into method call environments before evaluating the method body. This makes method calls behave more like standard function calls and makes method code easier to analyze correctly. For now, attempts to use these variables in a method will signal an error; this will eventually be dropped.