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A general description is here.
‘structure(NULL, <name> = <val>)’ is now defunct.
Setting ‘attributes’ on primitive functions is an error now; previously, it modified without copying, as noticed by Henrik Bengtsson on the R-devel mailing list.
Relatedly, changing the ‘environment()’ of a primitive function does no longer happen and gives a warning (to become an error, later).
Setting ‘attributes’ on primitive functions is deprecated now and already an error in the development version of R.