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HoltWinters() now uses optimize() rather than optim for one-parameter problems which should be more reliable (PR#11469).
hasMethods(f, env) {without specified 'package'} now works better.
conformMethod(), called by setMethod(), now checks better about argument names in wrong order. Whereas it only warns currently, it is planned to become be an error in the future.
The predict() method for prcomp() had an incorrect check for the number of columns of 'newdata' if the columns were not named.
validObject() called with complete=TRUE did not use inherited validity methods for slot classes.
sSeveral bugs fixed in as(): the initial method lookup was not using the table with inherited methods (so inheritance had to be recomputed each time); coerce() should not be called directly--it can insert invalid inherited methods; the constructed as() methods were not retaining the function's environment.
plot(<glm>, which=5) uses more correct cCook's distance contours; (fix to fix to PR#9316).
pdf() and postscript() were not working correctly in 2.7.0 with UTF-8 encoded data in a non-UTF-8 MBCS (e.g. EUC-JP on Unix, CJK locales on Windows).