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A general description is here.
Rd conversion was handling expressions like '\item{foo}{see \eqn{x}}' (with one argument to \eqn immediately followed by a right brace) incorrectly, sometimes giving a spurious warning about 'missing text'.
R CMD INSTALL used the C locale to install the DESCRIPTION file, and so escaped non-ASCII characters in packages with a declared encoding of "latin1" or "UTF-8". (However, the installed DESCRIPTION file was rarely used since the dumped metadata are available.)