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A general description is here.
Calling ‘&&’ or ‘||’ with either argument of length greater than one is now an error. Environment variable ‘_R_CHECK_LENGTH_1_LOGIC2_’ can still be set to get a verbose report (although that is likely to be removed before release).
The default error report is of the form
'length = 4' in coercion to 'logical(1)'
The included BLAS sources have been updated to those shipped with LAPACK version 3.10.1. This makes some (platform-dependent) changes to package check output.
The included LAPACK sources have been updated to include the four Fortran 90 routines rather than their Fortran 77 predecessors. This too may give some different signs.
Setting environment variable ‘_R_CHECK_RD_VALIDATE_RD2HTML_’ to false value will override ‘R CMD check --as-cran’ and turn off HTML validation. This provides a way to circumvent a problematic ‘tidy’ such as the 2006 version that ships with macOS.
‘R CMD check’ can optionally (but included in ‘--as-cran’) validate the HTML produced from the packages ‘.Rd’ files. See <URL: https://blog.r-project.org/2022/04/08/enhancements-to-html-documentation/index.html> : this needs a fairly recent version of HTML tidy to be available.