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A general description is here.
‘sub’, ‘gsub’ and ‘strsplit’ now mark their non-ASCII results as
‘"bytes"’ when ‘useBytes = TRUE’ or any input is marked as ‘"bytes"’.
The performance of ‘grep’, ‘sub’, ‘gsub’ and ‘strsplit’ has been improved, particularly with ‘perl = TRUE’ and ‘fixed = TRUE’. Use of ‘useBytes = TRUE’ for performance reasons should no longer be needed and is discouraged. It may lead to incorrect results.