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‘c(a=1, 2)[[]]’ no longer matches ‘2’ but rather signals a _classed_ error. Reported and analysed by Davis Vaughan in PR#18367, a duplicate of PR#18004, by Jan Meis et al. For consistency, ‘NULL[[]]’ is also erroneous now. ‘x[[]] <- v’ gives an error of the same class ‘"MissingSubscriptError"’.