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A general description is here.
'Writing R Extensions' now stresses that the standard sections in '.Rd' files (other than '\alias', '\keyword' and '\note') are intended to be unique, and the conversion tools now drop duplicates with a warning.
The '.Rd' conversion tools also warn about an unrecognized type in a '\docType' section.
'ecdf()' objects now have a 'quantile()' method.
'format()' methods for date-time objects now attempt to make use of a '"tzone"' attribute with '"%Z"' and '"%z"' formats, but it is not always possible. (Wish of PR#14358.)
'parse()' did not backquote some default arguments in the '\usage' section. (Reported by Claudia Beleites.)