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A general description is here.
‘R CMD check’ now runs sanity checks on the use of ‘LazyData’, for example that a ‘data’ directory is present, that ‘LazyDataCompression’ is not specified without ‘LazyData’ or that ‘LazyDataCompression’ is specified with a default value. For packages with large LazyData databases without specifying ‘LazyDataCompression’, there is a reference to the code given in ‘Writing R Extensions’ §1.1.6 to test the choice of compression (in all CRAN packages tested a non-default method was optimal).